Prepare 8-inch square glass pan rubbing bottom and sides with butter. Melt butter in a microwave-safe dish. Stir in brown sugar. Return to microwave for two minutes.
Mixture will be boiling. Slowly pour in cream and bourbon. Stir in powdered sugar. Spread into dish and cover with wax paper, lightly pressing into mixture.
Refrigerate for one hour. Grease a spatula to help lift hardened mixture onto a cutting board. Grease a knife to cut fudge into bite-sized pieces. Store in an airtight container.