Good-Cooking - German Sweet Chocolate Cake

Ingredients

• 4 ounces German chocolate
• 1/2 cup boiling water
• 1 cup butter or margarine
• 2 cups granulated sugar
• 4 egg yolks
• 1 teaspoon vanilla extract
• 2 1/2 cups sifted all-purpose flour
• 1 teaspoon baking soda
• 1 cup buttermilk
• 4 egg whites, stiffly beaten