Place the chopped chocolate in a large stainless steel bowl.
In a large, high sided saucepan, heat cream and butter over medium high heat, stirring frequently, until it just starts to boil. Watch carefully as it will boil over pan in a matter of seconds. Immediately remove from heat and pour over chopped chocolate.
Stir until chocolate is completely melted and mixture is smooth. Cool completely and then store in refrigerator. Ganache can be reheated in a double boiler over simmering water.