In a large mixing bowl, add the 1 2/3 cup all-purpose cake flour, 1 cup sugar, 1/2 teaspoon baking soda, 1 teaspoon baking powder, and mix well. Then in another bowl, add your wet ingredients, the 3/4 cup unsalted butter, 1/2 teaspoon salt, 3 large egg whites, 3 teaspoons pure vanilla extract, 1/2 cup sour cream, and 1/2 cup milk. Mix well. Mix in your 1/2 cup sprinkles.