6 large egg yolks, room temperature, lightly beaten
1-1/2 teaspoons vanilla extract
1-1/2 cups butter, softened
6 tablespoons confectioners' sugar
In a heavy saucepan, bring sugar and water to a boil; cook over medium-high heat until sugar is dissolved. Remove from the heat. Add a small amount of hot mixture to egg yolks; return all to the pan, stirring constantly. Cook 2 minutes longer or until mixture thickens, stirring constantly. Remove from the heat; stir in vanilla. Cool to room temperature.
In a bowl with the whisk attachment, cream butter until fluffy, about 5 minutes. Gradually beat in cooked sugar mixture. Beat in confectioners' sugar until fluffy, about 5 minutes. If necessary, refrigerate until frosting reaches spreading consistency. Store in the refrigerator.
Classic Chocolate Buttercream Frosting: Prepare buttercream frosting as directed above and set aside. In a saucepan or microwave, melt 1-1/2 cups semisweet chocolate chips with 1/4 cup water; stir until smooth. Remove from heat; cool to room temperature. Stir into buttercream frosting. Yield: 3 cups.