These cupcakes are brimming with rainbow confetti sprinkles and taste just like vanilla birthday cake! A pocket of sunny pineapple filling is the surprise inside.If you're not up to making the cloud decors, a simple topping of rainbow sprinkles makes a fine presentation on its own.
Preheat oven to 350°F. Prepare a cupcake pan with silver foil cupcake liners and set aside.
In a large mixing bowl, cream butter and sugar together until light and fluffy, about 3-4 minutes. Add sour cream and mix until well combined. Add egg whites, one at a time, mixing until well combined after each addition. Scrape down the sides of the bowl to be sure all the ingredients are well incorporated.
Combine the flour, baking powder and salt in a separate bowl, then combine milk and extract together in a small measuring cup. Add half of the dry ingredients to the creamed butter mixture and mix until just combined. Add the milk mixture and mix until well blended. Add the remaining flour mixture and beat until just combined; scrape down the sides of the bowl to make sure that all the ingredients are well incorporated. Fold in the sprinkles.
Fill the prepared pan and bake for 15-17 minutes, or until a toothpick inserted comes out clean. Let cupcakes cool in the pan about 5 minutes, and then remove to a wire rack to cool completely.
Pineapple Filling
In a medium saucepan, whisk together the cornstarch, sugar and salt. Stir in the crushed pineapple with juice. Cook over medium heat until the mixture bubbles, stirring constantly. Cook the mixture for 5 minutes, or until thickened. Remove from heat and stir in the butter. Let cool slightly then transfer to a bowl and let chill in the refrigerator. Cool completely before using.
Cut a divot from the centers of each cupcake and fill with a spoonful of the cooled pineapple filling. Trim cut out pieces flat and replace on top of the filled cakes.
Buttercream and Decors
In a stand mixer fitted with the whisk attachment, mix together the butter and confectioners’ sugar. Begin on low speed until crumbly, and then increase to high and beat for 3 minutes.
Add vanilla extract and beat again for another minute. If you find the buttercream is too stiff, you may add milk or heavy cream 1 tablespoon at a time until the mixture is spreading consistency. Fold in sky blue food color a little at a time until a vivid blue color is achieved. Transfer the frosting to a piping bag fitted with a large French decorator piping tip.
Pipe swirls of frosting on top of the filled cupcakes and immediately top with rainbow sprinkles. Stand a cloud cupcake topper upright in the piped frosting. Garnish with stars. Serve cakes immediately. Refrigerate leftovers in an air-tight container. Bring cupcakes to room temperature before serving.