Can You Substitute Margarine For Butter In Buttercream Frosting Ingredients 3 Cups Powdered Sugar 1 3 Cup Butter Or Margarine Softened 1 1 2 Teaspoons Vanilla 1 To 2 Tablespoons Milk Directions 1 In Vanilla Buttercream Frosting Vegan Sour Cream Buttercream Frosting