Combine chocolate, milk and sugar in heavy saucepan.

Heat chocolate, milk and sugar in a heavy saucepan, stirring constantly until chocolate is melted and the mixture comes to a boil.

Remove from heat and add butter and vanilla.

Stir until butter is melted and incorporated into the chocolate sauce.

Let cool for 5 minutes to thicken before serving.

May be stored in the refrigerator for up to 2 weeks if it lasts that long!