Here are two traditional buttercream recipes I've used on wedding cakes -
Vanilla Buttercream
1 cup sugar
1/2 cup water
4 egg whites (about 1/2 cup)
1 teaspoon vanilla
2 cups butter, cut up
In a saucepan, place the sugar and carefully pour the water around the edge. Using your finger, make an X in the pan to help the water gently mix with the sugar. Bring to a boil and cook to softball stage (235 degrees F.)
Meanwhile, whip the egg whites in a mixer with a whip attachment until light and fluffy. When sugar is at the softball stage, slowly pour it into the bowl down the side and continue whipping, adding vanilla, until incorporated and then cooled.
Add the butter 1 cube at a time while whipping until it is a thick butter cream (check flavor and consistency of butter cream before continuing to add butter, as not all of the 2 cups may be needed).
Keep at room temperature while frosting the cake.
***********************************
CHOCOLATE BUTTERCREAM
makes 3 cups
1 cup sugar
1/3 cup water*
1 ½ tsp. vanilla
2T liquer*
4 oz. semisweet chocolate melted, cooled
11/2 cups soft butter
6 beaten egg yolks
*if using liqueur, reduce water to ¼ cup
In heavy saucepan, combine sugar and water; bring to a boil; remove from heat; gradually stir a little of the sugar mixture into the beaten egg yolks; return all yolk mixture to saucepan; bring to gentle boil, reduce heat, cook and stir 2 minutes; remove fromheat; add liqueur; stir in vanilla. Cool to room temperature.
In mixer, beat butter on high speed til fluffy; add cooled chocolate and cooled sugar-egg mixture; beat til combined; chill til mixture is of spreading consistency.