Preheat oven to 350 degrees. Spray a cupcake pan with non-stick cooking spray.
Mix cake mix with pudding mix, eggs, water, melted butter, and sour cream in a large bowl on medium speed with a mixer, or beat vigorously by hand for 2 minutes.
Divide cupcake batter into the cupcake pan, filling all 12 cavities evenly. They will be full.
Bake for 20 minutes, or until an inserted toothpick comes out clean. Allow cupcakes to cool in the pan for 5 minutes, then carefully remove and place on a cooling rack.
Place cooled cupcakes in 8-ounce dessert cups or bowls.
Beat frosting ingredients together until creamy and smooth. Add additional heavy cream, if necessary, until the desired consistency is achieved.
Squeeze frosting over the cupcakes in the dessert cups and spread flat using a metal spatula or butter knife.
Press the tops of the cups into rainbow nonpareil sprinkles.
Video
Notes
Store dot cakes at room temperature or chilled for up to 5 days.