This Doughnut Cake With Mocha Whipped Cream is made from layers of homemade sour cream doughnuts and a light, fluffy mocha whipped cream. The result is a gorgeously unique layer cake that’s the stuff of Homer Simpson’s dreams!
Sift the cake flour, baking powder, salt, and nutmeg together in a bowl.
Combine the granulated sugar and butter in the bowl of a large stand mixer fitted with a paddle attachment. Cream them together until the sugar is moistened and it's the texture of wet sand. Add the egg yolks one at a time, and mix until the mixture is thick and light.
Turn the mixer speed to low and add a third of the flour mixture. When it is mostly mixed in, and just a few streaks of flour remain, add half of the sour cream. Continue to alternate adding flour and sour cream until everything is added. Stop the mixer when there are just a few streaks of flour left and scrape down the bottom and sides of the mixing bowl. The dough will be sticky.
Transfer the dough to a clean bowl, cover it with cling wrap, and refrigerate it for an hour to chill.
Once chilled, lightly flour your work surface and roll out the dough until it is a little thicker than 1/4". Cut out circles about 1-1/4" wide using a small circular cutter, then cut a hole in the center about 1/2" wide. (I used the top of a large piping tip, Ateco #807, to make these small holes. A small round fondant cutter would also work well.) Re-roll the scraps and continue cutting the doughnuts. I got about 90 small doughnuts from this batch.
Pour the oil into a large saucepan until it's about 1 1/2-2" deep. Insert a deep fry thermometer and heat the oil over medium heat until it is 325 F. During the frying process, you'll want to monitor this temperature carefully, and take the pan off the heat if it starts climbing too high. It's important that this temperature remain steady so your doughnuts cook properly, so try always to maintain around 325 F.
Fry the doughnuts in small batches until they're puffed and golden, making sure not to overcrowd the pan. It should only take about 1 minute on each side. Cover a baking sheet with paper towel, and transfer the cooked doughnuts to the sheet to let the excess oil be absorbed. Continue until all of the doughnuts have been fried. Let them cool completely before assembling the cake.
To Make the Whipped Cream and Assemble:
Pour the cream into a chilled mixing bowl. Sift the powdered sugar, cocoa and espresso powder over the cream, and add the vanilla extract. Whip until the cream holds firm peaks.
Place a cake cardboard in the bottom of a 7-inch springform pan. Place a 4-inch acetate cake collar around the inside of the pan. If you don't have an acetate collar, you can form a tall ring with aluminum foil—you just need something to extend the top of the springform pan about 4 inches. You can also use a different size of springform pan, just be aware that you may not get the same number of layers if you make a larger cake.
Spread a thin layer of mocha whipped cream on the bottom of the cake cardboard. Arrange a ring of doughnuts around the edge of the cardboard, then fill in the center with more doughnuts, cutting some if necessary to try and cover as much of the space as possible. Top this layer of doughnuts with a thick layer of mocha whipped cream, spreading it out almost to the edge of the cake. Add another layer of doughnuts, then continue to alternate layers of cream and doughnuts until you have four layers of doughnuts total.
Top the top layer of doughnuts with more whipped cream, spreading it into a smooth, even layer on top. Cover the cake with a loose tent of plastic wrap, and refrigerate it overnight so the doughnuts soften and everything melds together.
To Make the Chocolate Ganache:
Pour the cream into a small saucepan and add the espresso powder, and turn the heat to medium-high. Place the chopped semi-sweet chocolate in a medium bowl nearby. Bring the cream to a simmer, so that bubbles appear along the side of the pan.
Pour the hot cream over the chopped chocolate, and let it sit for one minute to soften the chocolate. Whisk them together gently until the mixture is shiny and smooth. Press a layer of cling wrap on top and let sit at room temperature until you're ready to use it.
To Finish the Cake:
Unclasp the springform pan and remove the cake from the pan. Unwind the acetate cake collar or foil collar from the sides of the cake, and place the cake on your serving platter.
If the ganache has firmed up too much to be easily pourable, warm it in the microwave in short 5- or 6-second intervals, whisking often, until it is liquid and flows easily. Pour it on top of the cake, and gently spread it to the edge of the cake so some of it drips down. Add sprinkles on top, if desired.
Refrigerate the cake for about 20 minutes to set the ganache. Once set, top with additional small doughnuts, whipped cream, or any other garnishes if desired.
The cake will need to sit overnight before you serve it, so be sure to take that into account when making this recipe. I recommend making the doughnuts, assembling the cake, and making the ganache on one day, then on the second day you can top the cake with ganache and sprinkles, and you're ready to serve it! If you want to make glazed doughnuts to go on top like I did, I recommend using the chocolate and vanilla glazes in this recipe. The doughnut recipe is adapted from the excellent book Top Pot Hand-Forged Doughnuts.