Good-Cooking - Red Velvet Cake

Ingredients

• 2 cups all-purpose flour
• 2 teaspoons baking powder
• 1 teaspoon cocoa
• 3/4 cup vegetable oil
• 1 1/2 cups granulated sugar
• 2 eggs
• 1 (1 ounce) bottle red food color
• 1 1/3 cups buttermilk
• 1 teaspoon baking soda
• 1 teaspoon vinegar
• 1 teaspoon vanilla extract
• 5 tablespoons flour
• 1 cup milk
• 1 cup margarine
• 1 c sugar