In medium skillet, sauté
mushrooms, onion, and garlic in butter until tender, about
2 minutes. Combine ground pork, mustard, Worcestershire
sauce, salt, and pepper; mix well. Shape into 12 patties,
about 4 inches in diameter. Set aside. Spoon equal portions
of mushroom mixture onto center of 6 pork patties. Spread
to within 1/2 inch of edge. Top with the remaining 6 patties;
seal edges. Place patties on grill about 6 inches over
medium-hot coals. Grill 10–15 minutes, turning once.
Serve on buns, if desired. Serves 6.