Chocolate Mint Patties

Bring a couple inches of water to a simmer in the bottom of a double boiler. Combine butter and whipping cream in the top of a double boiler and place over simmering water. Stir until melted. Add frosting and heat, stirring frequently, for 15 minutes, or until thickened. Stir in peppermint extract and remove from heat. Working quickly, drop by the teaspoonful into small paper cups or onto wax paper. Make a swirl design on the top of each candy with a spoon or fingertip. Cool completely.