This is my favorite cake frosting. I double it for a 2-layer cake.
Vanilla Buttercream Frosting
1 stick softened butter (8 T.)
1 1/2 cup powdered sugar
1/2 t. pure vanilla extract
With an electric mixer, beat the butter until light and fluffy. On medium speed, beat in the powdered sugar, 1/2 cup at a time. Scrape down the bowl as necessary. Mix in vanilla. Increase speed to high and beat until light and fluffy about 5 minutes.
To make raspberry buttercream frosting, add 3-4 teaspoons of raspberry jam to the above recipe.
To make chocolate buttercream frosting, add 4 oz. melted bittersweet chocolate to the above recipe.