To cook over a gas grill, preheat grill according to manufacturer's directions for medium heat. Grill patties and polenta, covered, 9 to 10 minutes or until patties are medium (160 degrees F) doneness, not pink in center and juices show no pink color and polenta is heated through, turning once and basting patties with 2 tablespoons reduced vinegar after turning. If prepared polenta is not available, the following may be used: Combine 3 cups water, 1 tablespoon butter and 1/2 teaspoon salt in large saucepan and bring to a boil. Gradually whisk in 1 cup cornmeal. Reduce heat to medium-low; cook 15 minutes, stirring often. (Mixture will be very thick.) Remove from heat; cool slightly. Spoon polenta on aluminum foil-line baking sheet. Cover with plastic wrap and pat into 12 by 6 by 1/2-inch rectangle. Refrigerate 1 hour or as long as overnight. Cut chilled polenta into 8 (3-inch) circles using a cookie or biscuit cutter. Proceed as directed above. Prepared balsamic syrup, available in large supermarkets and specialty food stores, may be substituted for balsamic reduction.