In a stand mixer, whip the whipping cream with a beater attachment until soft peaks form. Add frosting, liqueur, and peppermint extract to the whipping cream and beat just until firm peaks form. Spoon the mousse mixture into an icing bag fitted with a large star tip. Pipe mousse mixture into the center of each cookie cup. Sprinkle with crushed chocolate chips, if desired. Serve immediately or store in refrigerator until ready to serve.