Preheat oven to 375 degrees F. Beat vegetable oil spread and the butter in a large bowl with an electric mixer on medium to high speed for 30 seconds. Gradually add sugar, about 2 tablespoons at time, beating on medium speed until well mixed, scraping side of the bowl constantly. Beat on medium speed for 2 minutes more. Gradually add the egg whites, beating well. Beat in vanilla. Alternately add the flour mixture and milk to the butter mixture, beating on low speed after each addition just until combined. Spread the batter into the prepared pans.