1 (14 ounce) can sweetened condensed milk
4 (1 ounce) squares semisweet chocolate (or use same amount of semi sweet chocolate chips)
2 tablespoons butter (don't substitute)
1 teaspoon vanilla extract
In a heavy saucepan, combine the milk, chocolate and butter. Cook and stir over medium-low hat until chocolate is melted. Remove from the heat; stir in vanilla.