Make your own homemade cake mix, then make a white cake from that mix. It's easy to make your own mix, less expensive, and good for you—and you control the ingredients!
Preheat oven to 350 F. Spray two 8" round cake pans OR one 13" x 9" cake pan with a nonstick baking spray containing flour and set aside.
Pour one portion of the cake mix into a large bowl. Make a well in the center of the mix and add vanilla, oil, egg whites, and milk. Beat mixture 1 minute with an electric mixer at low speed until blended. Scrape sides and bottom of the bowl and beat 2 minutes longer at medium speed until batter is smooth.
Pour into prepared pans and bake the layer cakes at 350 F for 20 to 30 minutes, or until cake springs back when pressed lightly in center and begins to pull away from edges of the pan. Bake the 9" x 13" cake for 25 to 35 minutes until the cake tests done.