In a sauce pot, over medium- low heat, melt butter and chocolate.  Don't leave the pan, chocolate can burn really quickly and there is no recovering from that!  Add Sugar, milk and cream and stir to combine.  Keep stirring until smooth.  Add vanilla and a pinch of salt.

Martha Tip:  Always add the vanilla in at the end.  If you add too soon it will evaporate and the flavor will be less intense.