In a medium saucepan, heat chocolate and butter over medium heat. Cook, stirring frequently, until chocolate is melted and mixture is smooth. Stir in sugars. Add cream; bring to a boil over medium-high heat. Reduce heat, and simmer for 5 minutes, stirring frequently. Remove from heat, and stir in vanilla. Cover and refrigerate for up to 1 week.
Recipe by The Ribbon in My Journal - Phyllis Hoffman DePiano at https://www.theribboninmyjournal.com/happy-national-pound-cake-day/