Chocolate Dessert Topping

           1/2 cup butter
           12 ounce evaporated milk
           2 cups powdered sugar
           2/3 cup chocolate chips
           1 teaspoon vanilla

           In a large sauce pan melt butter over
           medium heat. Add evaporated milk; mix
           well. Add powdered sugar and chocolate
           chips. Bring to a boil, stirring often. Boil
           for 8 minutes; stirring constantly. Remove
           from heat, add vanilla, mix well.