Deb, This recipe is also from The Cake Bible by Rose Levy Beranbaum.

Neoclassic Buttercream
Makes 4 cups

"This is an easier technique than that for classic buttercream and yields identical results. In the neo classic method, some of the sugar and all of the water is replaced by corn syrup. The corn syrup provides just the right amount of water so that, when brought to a full rolling boil, the temperature of the syrup is exactly 238 degrees F. There is no need to use a thermometer. The corn syrup also prevents crystallization." "One recipe can accomodate as much as 1/2 cup liquid without becoming too soft."

The Buttercream

6 large egg yolks at room temperature
3/4 c. sugar
1/2 liquid c. corn syrup
2 c. softened, unsalted butter
optional: liquer or eau-de-vie of your choice

Have ready a greased 1 cup heatproof glass measure near your stove.

In a bowl beat the yolks with an electric mixer until light in color. Meanwhile combine the sugar and cornsyrup in a small saucepan(preferably with a nonstick lining) and heat, stirring constantlym until the sugar dissolves and the syrup comes to a rolling boil. (The entire surface will be covered with large bubbles.) Immediately transfer the syrup to the glass measure to stop the cooking.

If using a hand-held mixer, beat the syrup into the yolks in a steady stream. Don't allow the syrup to fall on the beaters or they will spin it onto the sides of the bowl. If using a stand mixer, pour a small amount of syrupover the yolks with the mixer turned off. Immediately beat at high speed for 5 seconds. Stop the mixer and add a larger amount of the syrup. Beat at high speed for 5 seconds. Continue with the remaining syrup. For the last addition, use a rubber spatula to remove the syrup clinging to the glass measure. Continue beating until completely cool.

Gradually beat in the butter and, if desired, any optional flavoring. Place in an airtight bowl. Bring to room temperature before using. Reheat to restore texture. *Do not reheat chilled buttercream until it has reached room temperature or it may curdle.

Store 6 hours at room temperature, 1 week refrigerated, 8 months frozen.

Pointers for success: The syrup must come to a rolling boil or the buttercream will be too thin. Don't allow the syrup to fall directly on to the beaters as it will spin the syrup around the sides of the bowl. Using a hand-held mixer makes this easier.