In a small saucepan, combine currant jelly, ketchup, vinegar, cinnamon, and cloves. Cook and stir just until boiling. Remove from heat; cover to keep warm.
In a medium bowl, combine egg, bread crumbs, onion, milk, salt, thyme, and pepper. Add ground pork; mix well. Shape mixture into four 3/4-inch-thick patties.
For a charcoal grill, place patties on the rack of an uncovered grill directly over medium coals. Grill for 14 to 18 minutes or until done (160 degrees F), turning once halfway through grilling. Toast hamburger buns on the grill. (For a gas grill, preheat grill. Reduce heat to medium. Place patties, then hamburger buns on grill rack over heat. Cover and grill as above.)
Serve burgers in buns with lettuce (if desired) and sauce. Makes 4 servings.