350°F oven. Grease two 8-inch circular cake pans. Grease circular parchment paper on the bottom of each cake pan
Whisk egg whites, 1/4 cup milk, and vanilla in a measuring cup. Reserve.
Mix dry ingredients on low speed for 30 seconds in a stand mixer with a paddle attachment.Add butter and the remaining 1/2 cup milk
Mix slowly until moistened. Mix medium-speed for 1 1/2 minutes.Scrape bowl sides.
Add the egg mixture in three batches on medium speed, beating for 20 seconds after each addition.
Bake until a toothpick inserted in the centre comes out clean, 20–30 minutes. Beware of overbaking! Cool pans for 10 minutes.