01 - Chop the chocolate bar into small, uniform pieces to promote even melting.
02 - Place chopped chocolate and unsalted butter, if using, into a heatproof bowl.
03 - Set the bowl over a saucepan of barely simmering water ensuring the bowl bottom does not touch the water, stirring gently until chocolate is nearly melted.
04 - Remove from heat and incorporate heavy cream and vanilla extract if desired, stirring until smooth and glossy; add a pinch of sea salt to enhance flavor if preferred.
05 - Use immediately as a sauce or dip. If sauce thickens upon cooling, gently rewarm over the double boiler before serving.