Preheat the oven to 350 degrees F (180 degrees C). Grease a 10x15-inch jelly roll pan and line with parchment paper.
Sift cake mix into a large bowl to break up any lumps. Pour carbonated drink into the bowl; stir gently, just until combined. You want to trap some of the carbonation into the cake batter. Pour batter into prepared jelly roll pan.
Bake in the preheated oven until a toothpick inserted near the center comes out clean, 18 to 24 minutes. Cool cake in the pan to room temperature.
Next, cut 3 cake layers from the sheet of cake for each cake cup. How you cut layers will depend on the container you choose. You can use the actual container to cut layers, or you can use square or round cookie cutters. If the container you will assemble the dot cakes in is tapered, you will have to cut smaller layers for the bottom and middle layer than for the top.
Once cake layers are portioned out, place first layer in bottom of container, then spread with 1 tablespoon vanilla frosting. Add middle cake layer; spread with 1 tablespoon vanilla frosting, the add top layer of cake. Add 1 tablespoon frosting, level off frosting with a spatula, and top frosting to cover completely with nonpareils.
