Preheat the oven to 350, and spray the bottoms of four 8-inch cake pans with non-stick spray.
In the bowl of your stand mixer fitted with the paddle attachment, beat the butter and sugar on medium speed for 10 minutes, scraping the bowl occasionally, until very light and fluffy. Beat in the egg whites, one at a time, beating each for about 15 seconds before adding the next egg white. Scrape the bowl down and beat for 15 more seconds.
In a separate bowl, sift together the cake flour, baking powder and salt. In another bowl, whisk together the buttermilk, sour cream, vanilla and almond extracts.
With the mixer on low, add the flour mixture in three additions, alternating with the buttermilk mixture, starting and ending with the flour, being careful not to over-mix. Add the sprinkles and use a large spatula to briefly fold the sprinkles in, as well as any remaining bits of flour.
Divide the batter between the pans, weighing each to make sure the batter is evenly divided. Use a spatula to smooth out the top of the batter.
Bake the cakes on the center rack for about 28-30 minutes, until a toothpick in the center comes out clean or with moist crumbs clinging to it, and the centers spring back when lightly touched.
Set the pans on a wire rack, cover loosely with a clean kitchen towel, and cool completely before frosting. As the cake cools, it's normal for it to pull away from the sides of the pan, and for the top of the cake to settle and flatten, since this is a slightly dense, butter-based cake.