Preheat oven to 350°F. Prepare 3 round 8-inch cake pans by brushing with homemade pan release* (goop), lining with parchment rounds and brushing on more goop.
Place cake flour, sugar, baking powder and salt in a medium bowl. With an electric mixer on low, combine the dry ingredients for about 20 seconds.
Take the butter out of the refrigerator. With the mixer on low, add the butter, one cube at a time. Mix on low until you have achieved fine crumbs.
With mixer on low, add the milk and vanilla. Continue to mix on low for 5 minutes. Then gradually add the egg whites in several batches. Mix on low for 3 more minutes.
Pour batter into prepared pans with equal amounts in each pan (about 1 1/2 cups or 388g per pan). Bake for 25 minutes or until a toothpick inserted in center comes out clean (a few crumbs on toothpick is ok). DO NOT OVERBAKE! Let cakes cool in the pans for 15 minutes. Then remove from pans and cool completely on cooling racks. Frost when cooled. Store in an airtight container at room temperature for 1-2 days. To keep fresh longer, store in airtight container in refrigerator.
*Goop is homemade pan release. You can easily make it by combining 1/2 cup vegetable shortening (such as Crisco), 1/2 cup vegetable oil and 1/2 cup flour in the bowl of an electric mixer. Beat on medium speed until smooth and creamy. Brush on pans to prevent sticking. Store in the refrigerator in an airtight container for months. Or you can use non-stick cooking spray. To cut the parchment circles, place a clean pan on top of parchment paper. Use a sharpee marker to trace the outer edge of pan onto paper. Cut with scissors.