1. Place the meat in a bowl. Add the onion, 1 tablespoon ketchup, Worcestershire sauce, thyme, salt, and pepper and mix lightly with your hands.

2. Form the meat into 6 thick patties, about 3 inches across and 1½ inches thick. To stuff the burgers, remove some of the meat from the top center of each patty, insert a chunk of the blue cheese (flattened slightly with the palm of your hand if necessary), and re-cover with the meat.

3. Heat the oil in a nonstick skillet over medium-high heat. Cook the burgers, in batches if necessary, for 5 minutes on the first side; then turn and cook for 3 minutes on the second side for a crusty outside and medium-rare interior. Cook longer if you prefer your burger well done. Place the burgers on the toasted rolls, and serve with ketchup and the relish.