Preheat oven to 350°F. Grease and line three 8-inch pans with parchment.
Mix half the buttermilk with oil and sour cream. In another bowl, whisk egg whites with remaining buttermilk, vanilla, and almond extract.
In a stand mixer with the paddle attachment, combine flour, sugar, baking powder, baking soda, and salt. Add butter and mix on low until the mixture looks like wet sand.
Add the buttermilk/oil/sour cream mixture. Mix on medium speed for about 1½–2 minutes, or until the batter looks thick and creamy. Do not overmix.
Add the egg white mixture in three additions, scraping the bowl each time.
Fill pans about ⅔ full (roughly 450–500 g batter per pan for 8-inch rounds).
Bake for 25–28 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs. Cakes should just begin to pull away from the pan edges.
Cool in pans 5 minutes, then wrap warm layers in plastic or cool completely on racks before frosting.