Combine marshmallows and milk in a 2 1/2 qt. glass mixing bowl. Microwave, uncovered, at power level high for 4 to 5 min. or until marshmallows melt and puff. Stir until smooth. Add chopped cherries and liqueur, blending throughly. Let cool to room temp. about 30 min. Fold whipped cream into marshmallow mixture and turn filling into prepared pie crust. Refrigerate for at least 4 hours. Garnish, if you wish, with additional whipped cream and maraschino cherry halves.