3 sq. unsweetened baking chocolate
1/2 c. (1 stick) butter
3 c. sifted confectioner's sugar
1 2/3 c. (tall can) evaporated milk
1 1/4 tsp. vanilla extract

Melt chocolate and butter in a medium saucepan. Remove from heat. Add sugar alternately with milk, about a third of each at the time, blending well after each addition. Place over medium heat and bring to a boil, stirring constantly. Then cook and stir about 8 minutes until mixture becomes thick and creamy. Remove from heat and stir in vanilla. Serve warm as a sauce.