To make a moist white cake, preheat the oven at 350 degrees Fahrenheit, then gather together flour, milk, sugar, salt, butter, egg whites, vanilla extract and baking powder. Prepare a mixer and some cake pans to pour the cake batter into, or gather cupcake pans if making white cupcakes.
First, cream 1 cup of unsalted butter and 2 1/4 cups of sugar in a bowl. Then, mix 7 large egg whites, 1 cup of whole milk and 1 tablespoon of vanilla extract together in a separate bowl. Sift 1/2 tablespoon of salt and a tablespoon of baking powder into 3 cups of all purpose flour.
Mix the dry ingredients into the creamed butter mix slowly with a mechanical mixer using a low or medium setting. Then, add the liquid ingredients to the same bowl, and scrape the bowl while keeping the mixer on medium to maintain even ingredient distribution. Alternate adding dry and liquid ingredients until all the ingredients are added and the batter is smooth.
Fill the cake pans about halfway to avoid overflow during baking. Bake the cake mixture at 350 degrees Fahrenheit for about 25 to 35 minutes, adjusting the time according to the size of the pan.