Preheat oven to 350º F. Coat bottom and sides of a baking pan with non-stick baking spray, or butter and flour.
In the bowl of the stand mixer fitted with the paddle attachment add the cake mix and baking powder; mix to combine. Add the butter and mix on medium speed until the butter is incorporated, about 2 -3 minutes. Add aguafaba and mix to incorporate, scraping bowl as needed. Add milk and vinegar, increase speed to medium high and continue mixing for 2 more minutes. Foil in the sprinkles. Transfer batter to prepared pan.
Bake the cake following the box recommended bake times. I used a 9x9 square pan and I baked it for 30 minutes. When a toothpick inserted in the center comes out clean, the cake is done. Cool cake completely before frosting.
Prepare frosting following package instructions. Spread frosting over the cake and decorate with more sprinkles.
Notes
Aquafaba is just the liquid that we usually discard from the can of beans. This liquid emulates the unmistakably fluffy texture of whipped egg whites.I used 2 packages of frosting because I wanted to make a beautiful patter with the piping bag, but if you want to spread a simple layer of frosting 1 pack is enough.