1/4 lb. butter
1 lb. powdered sugar
1 1/4 c. heavy cream
1/2 lb. unsweetened chocolate
1/8 tsp. salt
1 tsp. vanilla

Combine all ingredients in top of double boiler. Cook over hot, not boiling, water for 30 minutes, stirring frequently. When well mixed and thickened, remove from heat and cool slightly. Then in two batches, put into blender container and blend until smooth.

Makes about 1 quart. This sauce needs to be served warm as it's very thick. If it has been kept for a while, it may need to be reheated and put into the blender again.