Melt 2 cups of the white chocolate chips in the microwave in 30-second bursts until smooth.
Fill each cavity of a silicone cold until covered. You can do this with a spoon drawing chocolate up the sides but a silicone pastry brush might help!
To make the Fireball ganache, combine the remaining 2 cups of white chocolate, the heavy cream and the Fireball in a microwave-safe bowl.
Very gently, remove the sphere halves from the molds.