6 large egg whites at cool room temperature
1 ½ cups sugar
4 tsp. baking powder
¾ tsp. salt
2 tsp. vanilla extract
2 1/3 cups cake flour
12 Tbsp. unsalted butter, softened but still firm
Place the flour, sugar, baking powder and salt in the bowl of a standing mixer fitted with the paddle attachment. Add the butter and ¼ of the milk mixture and mix on low speed until dry ingredients are moistened, about 1 minute. Increase the speed to medium and mix until the batter comes together, about 30 seconds. Increase the speed to medium high and mix for 2 minutes stopping to scrape down the sides of the bowl once or twice. Add the remaining milk/egg white mixture to the batter in three batches mixing for about 20 seconds after each addition. Scrape down the sides of the bowl and beat on medium high until batter is homogeneous and light, about 30 seconds longer.
Estelle's Sweet Tip: the recipe said not to cream the butter with the sugar, as most recipes require, but to beat the softened butter with the dry ingredients and then the wet ingredients. It said this results in a soft, moist and delicate cake!