Stir together first 4 ingredients until blended. Place 12 foil baking cups into muffin pans; spoon batter into cups.
Bake at 350° for 20 to 25 minutes. (A wooden pick inserted in center does not come out clean.) Cool in pans on wire racks 10 minutes; remove from pans, and cool completely on wire racks.
Return baking cups to muffin pans, and spoon ice cream evenly over each brownie. Freeze 8 hours or until firm.
Stir together whipped topping and, if desired, liqueur. Dollop evenly over ice cream. Freeze until ready to serve.
Pull a vegetable peeler down sides of mints, making tiny curls; sprinkle curls over cupcakes just before serving.
NOTE: For testing purposes only, we used Andes Creme De Menthe Thins for chocolate mints.