In a large bowl, combine the ground meat, peanut butter, butter, onion, egg and bread crumbs and knead with your hands until well combined.
Make patties about 4 inches wide and 3/4 inch thick.
Refrigerate for 1 to 2 hours to allow the patties to set and the flavors to meld.
Grill the burger on an outdoor grill for best results, or fry in a skillet with a small amount of olive oil for 2 to 3 minutes on each side, or until fully cooked inside.