Featuring light and fluffy cake layers that are exploding with rainbow sprinkles and slathered in a silky smooth cream cheese buttercream frosting, this is the Ultimate Funfetti Birthday Cake Recipe!!! Perfect for any special celebration or birthday party! This cake is sure to bring a smile to your face!
In a large mixing bowl, sift together the cake flour, baking powder, baking soda, and salt; set aside.
In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl using a handheld electric mixer, beat the butter on medium-high speed until smooth and creamy, about 1 minute.
Gradually add in the sugar. Once all of the sugar has been added, beat on high speed for 2 minutes.
Reduce the speed to low and add in the egg whites, a little bit at a time, beating well after each addition, and scraping down the sides and bottom of the bowl frequently.
In a spouted measuring cup, combine the milk, sour cream, oil, and vanilla. Mix until evenly combined.
On low speed, add the flour mixture in three additions, alternating it with the liquid milk/sour creamy mixture, beginning and ending with the flour, and mixing until just combined. Fold in the sprinkles.
Divide the batter evenly among the prepared pans and smooth the tops. (It should be about 765 grams of batter per pan).
Bake for 25 to 30 minutes, or until lightly brown around the edges and a toothpick inserted in the center of the cakes comes out clean.
Cool the cakes in the pans places on a wire rack for 15 minutes. Then invert the cake layers onto cooling racks and cool completely.
For the Cream Cheese Frosting:
In the bowl of a stand-mixer fitted with the paddle attachment, or in a large bowl using an electric handheld mixer, beat the cream cheese and butter on medium-high speed until completely smooth; about 2 minutes.
Reduce the speed to low and gradually add the sifted confectioners' sugar. Add in the salt and milk and beat until combined.
Once all of the ingredients have been incorporated, increase the speed to high and beat for 1 to 2 minutes, or until super fluffy.
Place 1/2 cup of the frosting in a piping bag that's fitted with a star tip. Set the rest aside to be used on the cake.
Using a long, serrated knife, slice each cake in half horizontally, so that you have 4 even layers.
Place one cake layer on a large plate or cake stand. Spread 2/3 cup of the frosting on top of the cake, covering it completely.
Top with another cake layer, and repeat the layering process, ending with the last cake layer on top. Spread all remaining frosting over the top and sides of the cake. Use the frosting in the piping bag to pipe stars on top of the cake and/or decorative swirls around the edges, as seen in my photos.
Using your hands, gently press some sprinkles around the sides of the cake.
Allow the cake to set for 20 minutes before slicing. Then slice and serve.