This Watermelon Layer Cake is the ultimate summer cake! Layers of watermelon-flavored cake are studded with mini chocolate chips, and the outside is painted to look just like a watermelon. It’s fun, it’s unexpected, and it’s really delicious—what more could you ask for?
I don’t know how to ease into this gently, so I’m just going to cut to the chase: I made a watermelon cake. As in, it looks like a watermelon. IT TASTES LIKE A WATERMELON. It also involves chocolate chips. It might be one of the most unexpected things I’ve made. Almost everyone who tried it was dubious at first, and gave me ~~skeptical eyebrows~~, but in the end they ended up going back for seconds. It’s a giant weirdo of a dessert, and I love it to pieces.
I’ve been wanting to make a watermelon cake for awhile now—it’s the perfect symbol of summer (my family is going through at least a melon a week around here!) and it’s such a fun and whimsical idea. Plus, as I learned from this Grapefruit Layer Cake, I really love the concept of turning big cakes into realistic pieces of fruit.
However, I also knew that I wanted my watermelon cake to taste like watermelon, and that part was a little trickier. Watermelon flavoring is pretty easy to buy online, but it’s not something that anyone already has in their pantry, and it’s probably not very available at most grocery stores, either. So instead, I opted to use watermelon gelatin (like Jell-O brand) to flavor the cake layers, with the thought that the gelatin is probably easier to come by. This might not be very accessible to international readers (sorrrrrrrry!) but I’m hopeful that it’s an easy find for some people, at least.
The gelatin worked like a charm! The watermelon flavor is pronounced and instantly recognizable, but not too overwhelming or candy-sweet. I kept the frosting a basic vanilla flavor, to balance it out a bit, and the chocolate chips—which were originally added just as a watermelon seed stand-in—were also a really nice addition! I never would have thought to pair watermelon and chocolate like that, but I ended up really liking the way the chocolate broke up the fruit flavor a bit.
So can we talk about the decorations now, or what?! I’ve seen lots of different versions of watermelon cakes, from really elaborate, realistic fondant-covered ones to very simple buttercream designs. I think my version falls in the middle of those extremes. It’s all buttercream, so you don’t have to stress about covering a cake in fondant, but it uses some hand-painting techniques to make that buttercream look FANCY. Plus it’s really fun to do!
I have a video below that shows how the buttercream painting is done, but the concept is simple: chill your cake well, and mix some green gel coloring with a splash of vodka to thin it out. Dip a natural sponge in the food coloring, then dab it on the sides of the cake in vertical stripes. Do the same thing with yellow coloring, blending the edges of the colors so your stripes become indistinct and the color distribution looks random and organic. I went over the green several times, to make some darker patches, and basically just dabbed at the cake with a sponge until I was happy with it. (It also helped to have a real watermelon nearby for inspiration. It’s amazing how, as soon as you’re trying to paint something, all memories of how it looks go flying out of your head!)
The good news is that in real life, watermelon patterns are really random and imprecise. So as long as you’re getting some green and yellow patches on the sides of your cake, chances are, it’ll look good! And did I mention it’s fun to do? Because it is. If you love to play with your food, this is the baking project for you!
[PS: DEFINITELY wear gloves while you do this, unless you want to creep people out with green fingers for the next few days. You’re welcome.]
Aside from the painted sides, the rest of the decorations consist of a few scattered black fondant seeds on top—but mini chocolate chips are a great substitute for the fondant-averse.
This really was such a surprisingly tasty and fun cake, and I wish I could share a slice with all of you to convince you of how good it is! Check out the video below showing how to make this cake, and PLEASE share pictures with me if you give it a try!
🎂 More Fun Party Cakes
- Circus Animal Cake
- Curious George Cake
- Mini Banana Split Cakes
- Striped Buttercream Balloon Cake
- Unicorn Cakes
- Piñata Cake
Birthday Present Mini Cakes
Striped Buttercream Balloon Cake
Watermelon Layer Cake
Ingredients
For the Watermelon Cake:
- 4 oz unsalted butter, (1/2 cup), at room temperature
- 4 oz vegetable oil, (1/2 cup)
- 14 oz granulated sugar, (2 cups)
- 4.5 oz powdered watermelon gelatin, like Jell-O brand, from 1.5 standard boxes
- 3 large eggs, at room temperature
- 1 tsp vanilla extract
- 13.5 oz all-purpose flour, (3 cups)
- 1 tbsp baking powder
- 2 tsp salt
- 12 fl oz buttermilk, (1 ½ cups)
- Assorted gel food coloring, I used a mix of Americolor brand colors: Super Red, Deep Pink, and Burgundy
- 6 oz miniature chocolate chips, (1 cup)
For the Buttercream:
- 6 fl oz pasteurized liquid egg whites, (3/4 cup)
- 24 oz powdered sugar, (6 cups)
- ½ tsp salt
- 24 oz unsalted butter, (3 cups) at room temperature
- 2 TBSP vanilla extract
- Assorted gel food coloring, I used Americolor brand: Leaf Green, Super Red, Deep Pink, Burgandy and Lemon Yellow
To Assemble and Decorate:
- 2 oz miniature chocolate chips, (1/2 cup)
- 1/3 cup vodka
- Black fondant, optional
Instructions
To Make the Watermelon Cake:
- Preheat the oven to 350 F. Line four 8″ round cake pans with parchment paper, and spray the pans with nonstick cooking spray.
- Combine the butter, oil, granulated sugar, and gelatin in the bowl of a large stand mixer. Mix on medium speed with the paddle attachment until light and fluffy. Add the eggs in one at a time, mixing well after each addition, then add the vanilla.
- Sift together the flour, baking powder and salt in a medium bowl.
- With the mixer running on low speed, add a third of the dry ingredients and mix until just a few flour streaks remain, then pour in half of the buttermilk. Continue to alternate adding dry and wet ingredients, ending with the drys. Stop right when the flour is mixed in.
- Finish mixing the batter with a rubber spatula, stirring around the bottom and sides of the bowl to make sure that all of the stray flour is incorporated. Add a few drops of red, pink, and burgundy food coloring, and stir well to incorporate it. Add additional color, as desired, until you get a nice watermelon shade.
- Divide the batter between the prepared pans. If you have a kitchen scale, each pan should get about 14 oz of batter. Sprinkle about ¼ cup miniature chocolate chips on top of each pan, and swirl them into the batter gently. Smooth the top of the batter.
- Bake the cakes at 350 F for about 30 minutes, until they start pulling away from the sides and a toothpick inserted into the center comes out clean. These cakes won’t dome much, so it’s better to use the toothpick test here. Let them cool completely before assembling the cake. They can be made in advance, wrapped well in plastic wrap, and stored in the refrigerator for up to 5 days or in the freezer for up to 4 weeks. If frozen, let them partially defrost before assembling.
To Make the Buttercream:
- Combine the whites, powdered sugar, and salt in the bowl of a large stand mixer fitted with a paddle attachment. Mix everything together on low speed, until the sugar is moistened and no dry patches remain. Turn off the mixer, scrape down the sides and bottom of the bowl with a spatula, then turn the mixer to medium speed. Beat on medium for 5 minutes.
- After 5 minutes, turn the mixer to medium-low and start adding the softened room temperature butter, 1-2 tablespoons at a time. Once all of the butter is incorporated, add the vanilla extract and mix it in. Stop the mixer and scrape down the bottom and sides once more. Turn the speed to medium and beat the buttercream for 10 minutes. At the end, you’ll have a frosting with a wonderfully light and creamy texture.
- Divide the buttercream in half. Color half of it with the red, pink, and burgundy colors to get a watermelon shade that matches your cakes. Leave the other half white for now.
To Assemble and Decorate:
- If you want to use black fondant to make seeds for the top of the cake, pinch off a tiny piece of fondant and roll it between your fingers to make it round. Press down to flatten it, then pinch the tip so it forms a seed shape. Repeat until you’ve made about 20 seeds. (If you don’t want to do this, you can substitute chocolate chips or mini chips instead.)
- Place one cake round on an 8” cake cardboard, and put it on a cake turntable. Add about a cup of red buttercream on top, and spread it out to the edges of the cake in an even layer. Scatter some miniature chocolate chips on top of the frosting, and use a spatula to swirl them into the buttercream.
- Place a second cake layer on top of the first, and repeat the frosting/chocolate chip/cake pattern until you’ve stacked all of the cake layers.
- Spread a layer of white buttercream all around the edges of the cake, leaving the top plain. The white will look like the watermelon’s rind when the cake is cut. Add enough buttercream so that the cake edges are completely covered and not peeking through. Refrigerate the cake for about 30 minutes to firm up the frosting. Place about 2/3 cup of white buttercream into a pastry bag fitted with a ½-inch round tip, and set aside.
- Tint the remaining white buttercream with a few drops of yellow and green food coloring, to make a light yellowish-green color.
- Spread this green buttercream in a thin layer over the white buttercream, just enough to cover it smoothly. Take the white buttercream in the piping bag, and pipe a ring of white frosting around the top of the cake, staying close to the edge.
- Put the remaining red buttercream on top of the cake, and spread the red out until it reaches the white frosting circle. Press your black fondant seeds (or chocolate chips) into the red frosting. Chill the cake well, for at least an hour, until the sides are very firm.
- Now for the fun part: painting the sides! I recommend wearing gloves for this step, unless you enjoy having bright green fingers. Mix together a teaspoon of green coloring with a tablespoon of vodka. Take a soft, new natural sponge and get it damp, then dip it into the food coloring. Dab the sponge on the side of the chilled cake in a vertical line, making a thick stripe. Make a second stripe, leaving a little space in between the two. Repeat around the sides of the cake, mixing together more food coloring and vodka if necessary, until you have green stripes all the way around.
- Rinse the sponge, and mix together yellow food coloring and vodka in the same way. Repeat the same procedure, adding yellow stripes in between the green ones. Dab the green and yellow together, to make them blend and make the stripes look more organic and less precise. Work the colors on top of each other, and don’t be afraid to add darker patches of green and yellow—the more random it is, the more natural it will look!
- For the best taste and texture, serve this cake at room temperature.
Video
Recipe Notes
Measuring Tips
Our recipes are developed using weight measurements, and we highly recommend using a kitchen scale for baking whenever possible. However, if you prefer to use cups, volume measurements are provided as well. PLEASE NOTE: the adage “8 oz = 1 cup” is NOT true when speaking about weight, so don’t be concerned if the measurements don’t fit this formula.
Want to learn more about baking measurements and conversion?
Do u think i could use strawberry whipped cream inside and whipped cream or white chocolate SMBC outside ir white ganache? Will ganache or whipped cream paint like buttercream will?
Hey Mimi, Whipped cream will not work well for the outside, you won’t be able to paint it. I would recommend the white ganache for the outside. You will just want to make sure it is chilled really well. You could fill it with whipped cream on the inside just fine. I would recommend a stabilized whipped cream to hold the weight of the ganache on the outside I have a recipe here https://www.sugarhero.com/strawberries-cream-layer-cake/ as an example. I would love to hear how it goes! If you have anymore questions feel free to let me know!
Make your seasonal summer to delicious use with this sweet and refreshing watermelon cake recipe. It look and taste like a real watermelon.
Hey Tokyo, I am so glad you like it! Thanks for your feedback!
How many people do you think this feeds? I need a cake for 20-30 people. Thanks!
Hey Jax, this recipe yields 20 servings however I think you could get more depending on the way you cut it and size of the pieces! I am so excited for you to make this! I hope it works out, and I would love to hear how it goes. I hope you enjoy it as much as we did!
Thank you. Enjoyed the video and learned a lot.
I’m thrilled to hear that, Deborah! Thanks for letting me know, and I’d love to hear how it goes if you give it a try.
Why gel food color? Will regular food color not work?
Hi Donna! Gel food coloring is much more intense, so the color payout is better. It is what I recommend for painting, but if regular food coloring is what you have, that will probably work but the appearance might not be the same.
I am making the watermelon cake and have a question— I will apply the stripes today – so after that when I attempt to move cake from decorating board to clean board or platter what is the best way to do this in order to avoid a mishap
Hi Donna! I suggest building the cake on a cardboard cake round that is the same size as your cake layers. When it is decorated, slide a metal offset spatula or a cake lifter under the cardboard round, and that way you can easily lift the cake and transfer it to a clean serving platter. Hope this helps!
Loved the recipe and tutorial . Will be making this cake for a dear friend who loves watermelon but think I will skip the flavored gelatin and just make it vanilla flavored . The frosting uses egg whites that are pasteurized so there is no fear of salmonella correct?, Will send a photo of my creation, hope it looks as great as yours! Thank you!
Cannot rate yet as I have not made the cake but it looks easy to do , just takes a little time and patience but results will be a “WOW” factor!
Hi Judie! Yes, you’re correct–the pasteurized egg whites mean that there is no danger of salmonella. You can also make a traditional Swiss meringue or just use an American buttercream recipe if the carton whites are hard to find. I’d love to hear how it goes if you give it a try, and feel free to reach out if you have any questions or run into problems!
Could I use something in place of vodka?
Yes, you can use clear lemon extract if you don’t want to use vodka. You just need something that will evaporate quickly, which alcohol will do. It might leave a slight lemon flavor but it’s usually not noticeable.
I Made this for my family and neighbors for a birthday party and they all loved it! Really recomend!
This review is for the decoration and frosting bit of the recipe ONLY. I decided to pass on the cake recipe because I was worried about the artificial/sweet type flavoring and opted for another sponge recipe that used watermelon juice and strawberry extract flavoring. The buttercream recipe is PHENOMENAL. I’m not a frosting kinda gal and this frosting is damned addicting and not at all the disgusting sweet profile that I usually associate with frosting. I’ve attempted a Swiss buttercream frosting before and failed both times. Starting with pasteurized egg whites and using powdered sugar seemed to be all the right hacks to get it right and boy did I get it right – soooooo goood. Thanks for the great instructions because it was easy to follow and soo much fun. I got all kinds of compliments and accolades about how impressive the cake looked. I was called a fancy mama several times *brushes shoulders off* the frosting procedure and layers were just so well thought out everyone loved eating it! Again this frosting recipe is such a winner and will be my go to from now on.