Ingredients
1¾cupscake flour,spoon & leveled
¾tspbaking powder
¼tspbaking soda
¼tspsalt
½cupunsalted butter,softened to room temperature
1cupgranulated sugar,(200 g)
3large egg whites,at room temperature
½cupfull-fat sour cream,at room temperature
2tsppure vanilla extract
½cupwhole milk,at room temperature
½cuprainbow sprinkles
1½cupsunsalted butter,softened to room temperature
6cupsconfectioners’ sugar
⅓cupheavy cream,or whole milk
2tspvanilla extract
⅛tspsalt
Preparation
Preheat oven to 350 degrees F. Grease three 6-inch cake pans, line with parchment paper, then grease the parchment paper.
Whisk the cake flour, baking powder, baking soda, and salt together. Set aside.
Using a handheld or stand mixer fitted with a paddle or whisk attachment, beat the butter and sugar together on high speed until smooth and creamy for about 3 minutes.
Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed. Beat in the egg whites on high speed until combined for about 2 minutes then beat in the sour cream and vanilla extract.
Scrape down the sides and up the bottom of the bowl as needed. With the mixer on low speed, add the dry ingredients just until combined.
With the mixer still running on low, pour in the milk and mix just until combined. Gently fold in the sprinkles.
Pour batter evenly into cake pans. Bake for around 18 to 21 minutes or until the cakes are baked through. To test for doneness, insert a toothpick into the center of the cake.
If it comes out clean, it’s done. Allow cakes to cool completely in the pans set on a wire rack.
In a large bowl using a hand-held mixer or stand mixer fitted with a whisk or paddle attachment, beat the butter on medium speed until creamy for about 2 minutes.
Add confectioners’ sugar, heavy cream, vanilla extract, and salt with the mixer running on low. Increase to high speed and beat for 3 minutes.
Add more confectioners’ sugar if frosting is too thin, more cream if frosting is too thick, or a pinch more of salt if frosting is too sweet.
Using a large serrated knife, slice a thin layer off the tops of the cakes to create a flat surface. Discard. Place 1 cake layer on your cake stand, cake turntable, or serving plate.
Evenly cover the top with about ¾ cup of frosting. Top with the 2nd cake layer and evenly cover the top with about ¾ cup of frosting.
Top with the third cake layer. Spread the remaining frosting all over the top and sides or, to replicate the decoration in the pictures and video, follow my directions in the recipe notes below.
Refrigerate for at least 30 to 45 minutes before slicing.
Cover leftover cake tightly and store in the refrigerator for 5 days.
