MELT butter in small saucepan; ADD chocolate and STIR constantly over hot water (or very low heat) until melted.
POUR into a small mixer bowl; ADD remaining ingredients; BEAT until well-blended.
CHILL until of spreading consistency (10 to 15 minutes).
Fills and frosts 8- or 9-inch layer cake or 13 x 9-inch cake.
Per Serving (excluding unknown items): 369 Calories; 14g Fat (32.3% calories from fat); 2g Protein; 65g Carbohydrate; 2g Dietary Fiber; 17mg Cholesterol; 157mg Sodium. Exchanges: 1/2 Grain(Starch); 0 Lean Meat; 0 Non-Fat Milk; 3 Fat; 4 Other Carbohydrates.