Preheat oven to 350°F (177°C). Grease three 8-inch or 9-inch cake pans, line with parchment paper rounds, then grease the parchment paper.

Whisk the cake flour, baking powder, baking soda, and salt together in a large bowl. Set aside.

Using a handheld or stand mixer fitted with a paddle attachment, beat the butter and sugar together on high speed for 5 full minutes until completely creamed together and fluffy.

Add the oil and beat for 1 minute until combined. Add the eggs, egg whites, and vanilla extract and beat on medium-high speed until combined.

Add dry ingredients and buttermilk in three additions, mixing after each addition just until incorporated. Gently fold in the sprinkles. Pour and spread the batter evenly into each cake pan.

Bake for around 25–26 minutes or until the cakes are baked through. Allow cakes to cool in the pans set on a wire rack for 20 minutes.

Run a knife around the edges and then remove cakes from pans. Place cakes directly on wire racks to cool completely.

In a large bowl using a handheld mixer or stand mixer fitted with a whisk or paddle attachment, beat the butter on medium speed until creamy, about 2 minutes.

Add confectioners’ sugar, cream, vanilla extract, and salt. Beat on low speed for 30 seconds and then switch to high speed and beat for 2 minutes.

Slice a thin layer off the tops of the cakes to create a flat surface. Place one cake layer on your cake stand, cover the top with about 1 cup of frosting. Repeat with second cake layer.

Spread a thin layer of frosting on the top and around the sides as a crumb coat. Chill uncovered in the refrigerator for at least 30 minutes.

Spread the remaining frosting all over the top and sides. Garnish with extra sprinkles, if desired.

Serve cake immediately, or store it for a few hours at room temperature. For longer storage, refrigerate covered cake for up to 1 day.