Chocolate Sauce

1 cup sugar
4 Tablespoons cocoa powder
pinch of cream of tartar
pinch salt
1/2 cup water
1 Tablespoon butter or margarine
1 teaspoon vanilla essence
Combine all the ingredients, except the butter and the vanilla by placing in a saucepan. Boil for 5 minutes.
Stir in the butter.
Add the vanilla.
Serve hot over ice-cream.