In a heavy medium saucepan, combine sugar, and cocoa powder. Stir in butter and buttermilk. Add bittersweet chocolate. Cook and stir over medium heat until chocolate is melted and mixture is smooth. Stir in whipping cream and corn syrup.

Cook and stir over medium heat for 4 to 6 minutes or until mixture just boils around edges. Remove from heat. Stir in vanilla. Cool slightly. Serve warm over ice cream. (Cover and chill any leftovers for up to 3 days. Sauce may also be frozen in a freezer container up to 1 month. Thaw before serving. To reheat sauce in your microwave oven, allow 60 seconds on high power for each cup, stirring once.) Makes about 3 cups sauce.

Prepare as above, except add 2 to 3 tablespoons amaretto, coffee liqueur, dark rum, creme de cacao, brandy or other desired liqueur with the vanilla. Makes about 3 cups sauce.

Prepare as above, except add 1 to 2 tablespoons espresso powder or instant coffee crystals with the vanilla. Makes about 3 cups sauce.

Prepare as above, except stir in 1/2 cup creamy or chunky peanut butter and 1/4 teaspoon ground cinnamon with the vanilla. Makes about 3 cups sauce.