Place white chocolate into a food processor and mix until chocolate is in small pea sized bits. Bring heavy cream to a simmer and pour over chocolate in food processor. Let the cream sit about one minute over chocolate then turn on food processor and let run until smooth. Add butter and Grand Marnier one at a time mixing until all bits of butter are incorporated. Remove form food processor into a small bowl cover and let set for 4 - 8 hours before using.
Use ganache as a filling in a favorite cookie, to decorate cakes and other confections, or as a truffle filling.