Preheat your oven to 350°.

Line the bottom of your 9x13x2 metal baking pan or 2 (9-inch) round cake pans pan(s) with parchment paper before spraying with nonstick spray with flour. Alternatively, you can butter and dust with flour.

Add homemade cake mix into a large mixing bowl or stand mixer, fitted with a paddle attachment.

In a separate bowl, whisk the egg whites, buttermilk and vanilla together before adding it to the cake mix. With your mixer on low speed, mix until just combined. Some small lumps are okay.

Lastly, add the sprinkles and use a rubber spatual to fold them in.

Pour the cake batter into the prepared pan and spread evenly.

Bake on the middl rack of your preheated oven for 30 to 35 minutes (20 to 25 minutes for for two 9-inch pans or 17 to 20 minutes cupcakes) or until a tester comes out with a few crumbs attached.

Let cool for 20 minutes before running a knife around the edge of the cake. Invert onto a wire cooling rack, remove parchment and cool completely. Once cooled completely, invert it back into the cake pan and frost with vanilla buttercream or frosting of your choice. before frosting.