Break the Chocolate bar into small pieces, place it in a medium size stainless steel bowl and set aside.
Heat cream in a medium flame to almost boil and add butter, sugar, vanilla essence and whisk quickly and frequently. Remove the mixture from the heat and slowly pour cream mixture over the chocolate chuncks. Whisk while pouring till the chocolate get fully melted and combined. If not using right away keep it in refrigerator. The chocolate sauce can be sed for sundae topping and ice cream.
To melt the Chocolate :
Melt the chocolate chunks in a double boiler. If a double boiler is not available, Let the water boiling in a medium size pan, putting chunks in another small pan and allow to melt it over the boiling water.