1 sq. unsweetened chocolate
1 c. sugar
1 c. milk
a "gob" of butter (probably about 1 tbsp.)
a pinch of salt
1 tsp. vanilla

Mix these (except vanilla) together and, while stirring, melt over a slow heat. If it boils, the sauce will form a shell on the cold ice cream and that's not all together bad. Take off the heat when melted and stir in vanilla. Spoon over ice cream and enjoy!