Heat oven to 350°F. In large bowl, place whipping cream, liqueur and chocolate-flavor syrup; refrigerate.
In medium bowl, place flour. Cut in butter using pastry blender (or pulling 2 table knives through ingredients in opposite directions), until evenly mixed. Stir in walnuts. In bottom of ungreased 9-inch square pan, press mixture evenly. Bake about 15 minutes or until light brown. Cool completely.
Beat whipping cream mixture with electric mixer on high speed until soft peaks form; spread over crust. Cover and freeze at least 4 hours or until firm but no longer than 48 hours.
Cut into about 3-inch squares. Store in freezer.