Pat pork chops dry with paper towels. Stir together 2 tablespoons thyme, peppercorns, 1 teaspoon salt, and garlic in small bowl. Rub mixture on both sides of chops. Let pork chops stand at room temperature for 30 minutes.

Preheat a charcoal or gas grill with greased grill rack for direct cooking over medium-high heat (375°).

Place onions in 12-inch cast iron skillet; top with butter. Arrange pork chops on top. Place skillet on grill rack. Grill 20 to 25 minutes or until pork chops reach 130°, turning halfway through. Remove pork chops from the skillet and place directly on grill rack. Grill 2 minutes or until lightly charred and pork reaches 145°, turning halfway through. Remove pork chops from grill; loosely cover with foil and set aside.

Add ale, beef broth, and Worcestershire sauce to onion mixture in skillet. Place skillet on grill rack; grill 30 to 35 minutes or until onions are golden brown, stirring frequently.

Place pork chops back into skillet with onion mixture. Grill 5 to 10 minutes or until pork chops are heated through. Garnish with thyme sprigs, if desired.