To Make the Whiskey Ganache Filling: Put chocolate chips into a heatproof bowl. Heat the cream in microwave for a minute, then for 30 second intervals until warm. Pour it over the chocolate. Let it sit for a couple minutes and then, using a rubber spatula, stir it from the center outward until smooth. Add the butter and whiskey (or vanilla) and stir until combined. Let the ganache cool until thick but still soft enough to be piped.