Melt margarine in large skillet. Add flour and all remaining crust ingredients to butter; cook over medium-high heat for 3 to 4 minutes or until mixture is crumbly, stirring constantly. Reserve 3/4 cup crumbs for topping. With back of spoon, press remaining mixture firmly in bottom of ungreased 9-inch square or 11x7-inch pan. Place in freezer for 10 to 15 minutes to cool.