1/2 c. sugar
1 1/2 tbsp. cornstarch
1 oz. square unsweetened chocolate
Dash of salt
1 1/2 tbsp. butter
1/2 tsp. vanilla

Combine sugar and cornstarch; add chocolate, salt and 1/2 cup water. Cook and stir until thickened and bubbly and chocolate melts. Remove from heat; add butter and vanilla. While hot, frost rolled cake.