1Place whipping cream, liqueur and syrup in large bowl; refrigerate.
2Heat oven to 350ºF. Cut butter into flour in medium bowl, using pastry blender or crisscrossing 2 knives, until evenly mixed. Stir in nuts. Press evenly in bottom of ungreased square pan, 9x9x2 inches. Bake about 15 minutes or until light brown. Cool completely, about 30 minutes.
3Beat whipping cream mixture with electric mixer on high speed until stiff; spread over crust. Cover and freeze at least 4 hours until firm. For serving pieces, cut into 3 rows by 3 rows; serve immediately. Store covered in freezer.