Preheat the oven to 350 F. Line cupcake pans with 24 liners. Sift together the flour, baking powder, baking soda, and salt in a medium bowl. Set aside for now.
Combine the butter and sugar in the bowl of a large stand mixer fitted with a paddle attachment. Mix on medium-high speed until light and fluffy, about 2-3 minutes.
Add the eggs one at a time, beating well after each addition, then add the vanilla extract. With the mixer running on low, add a third of the flour mixture, then when the flour streaks have disappeared, add half of the sour cream. Add half of the remaining flour, the rest of the sour cream, then finish with the last of the flour. Stop the mixer and scrape down the bottom and sides of the bowl with a rubber spatula to fully mix the batter.
Fill the cupcake tins until they're two-thirds full, then bake at 350 for 20-22 minutes, until they start to brown and a toothpick inserted into the center comes out clean. Cool the cupcakes completely before frosting.
To Make the Buttercream:
Place all of the ingredients in the bowl of a large stand mixer fitted with a paddle attachment. Mix on low speed until the sugar is moistened. Scrape down the sides of the bowl, then beat again on medium speed until light and fluffy, 2-3 minutes. You can add more milk or sugar, if desired, to get the consistency you want.
Melt the unsweetened chocolate in the microwave, then let it cool until it is barely warm to the touch. Divide the frosting in half, and mix the semisweet chocolate into one half to make chocolate frosting. Color the remaining half with a few drops of yellow food coloring.
Fit a piping bag with a coupler and a multi-opening tip. Fill the bag with the chocolate frosting. Pipe a swirl of frosting on top of the cupcakes, covering the top completely, then go around the edge of the cupcakes several more times, building up the sides so that the frosting looks like a nest.
Cut each Twinkie in half. Press half of a snack cake into the center of each frosting nest.
Tip: Depending on the size of your cupcakes, you may need to trim the cakes a bit more to get the best fit.
Fit a second piping bag with a coupler and a small star tip. Fill the bag with the yellow frosting. Pipe small stars all over each Twinkie until it is covered. Pipe a swoop onto each side of the cake for wings, and add a tail on top.
Press a round truffle on top of each Twinkie for the chick’s head. Refrigerate the cupcakes briefly to set the frosting, which will give you more stability to finish decorating the head. Pipe yellow frosting stars all over the surface of each truffle.
Cut the Starburst into four triangles each, and gently shape them until they are a beak shape. Press the candy beaks into the front of the chick's head, and finish by adding small round sprinkles for eyes.