1tbspclear imitation vanilla (this is essential for that old funfetti boxed cake flavor)
1cup (240 ml)milk
½cup (120 g)sprinkles of choice(I used Jimmies)
3cups (680 g)butter, at room temperature
6 cups (680 g)powdered sugar, sifted
1tbspvanilla extract(or seeds from one vanilla bean, 1 tbsp vanilla bean powder, or 1 tbsp vanilla bean paste)
sprinkles for decoration, as desired
FOR THE CAKE:
Preheat oven to 350°. Line the bottom of three 6-inch cake pans with parchment paper and spray with nonstick spray on paper and sides of pans. Set aside.
Whisk flour, cornstarch, baking powder, and salt in a medium bowl. Set aside.
In the bowl of a stand mixer (or a large bowl with handheld mixer), cream butter and granulated sugar on low until combined. Increase speed to medium high and cream until light and fluffy, about 3-5 minutes.
Reduce speed to low and add egg whites, one at a time. Stop mixer and scrape bottom and sides of bowl. Add flavorings and oil and beat to combine.
With mixer on low, add the flour mixture alternately with the milk. Don't overmix.
Right before scooping batter into pans, add ½ cup sprinkles to the batter and gently fold throughout. Scoop batter into pans. Bake for about 30-32 minutes, or until cakes spring back when touched lightly, or a toothpick inserted into center comes out mostly clean with only a few crumbs clinging to it (but no wetness). If cakes still aren't done at this point, keep checking at 2-minute intervals.
Remove from oven and cool in pans on wire rack for about 10 minutes. Use a butter knife to loosen cakes from sides of pans and flip over to cool completely on wire rack. OR immediately wrap warm cakes in plastic wrap and freeze. This makes it easier to fill and frost them.
FOR THE BUTTERCREAM:
Place butter in the bowl of stand mixer (or a large bowl with a handheld mixer) and using the flat (beater) blade, beat until creamy, about 2 minutes.
With mixer on low, slowly add sifted powdered sugar until all of the sugar has been added. Add vanilla extract and combine. Scrape sides and bottom of mixer. Turn mixer up to medium high and beat until light in color and texture, about 5-6 minutes.
Fill and frost cake as desired.
*to make this cake into cupcakes, line muffin pans with cupcake liners. Proceed as directed in recipe, but use a large scoop to scoop batter into cupcake liners. Begin checking at 20 minutes. If cupcakes spring bake when lightly touched or a toothpick inserted into center comes out clean, they are done. Cool. Decorate with frosting and sprinkles on top, or roll frosting completely in sprinkles. To do this, use a cookie scoop to place a scoop of frosting on top of the cupcake. Pour sprinkles in a small bowl. Flip the cupcake over so the frosting is resting on top of the sprinkles. Gently press each way to adhere the sprinkles to the frosting and create a "dome" shape.