Step 1

In a medium bowl, mix together the onion, garlic, parsley, mint, mustard, horseradish, Worcestershire, salt, cumin, pepper and egg. Add the lamb and mix well with your hands.

Step 2

Shape the lamb mixture into 4 patties. Press 1 tablespoon of the blue cheese into the center of each patty; roll into balls and then flatten into 3-by-1-inch patties. Transfer to a plate and refrigerate, uncovered, for at least 30 minutes and up to 2 hours.

Step 3

Heat a large cast-iron skillet over medium heat, then add the butter and canola oil. Place the cold patties in the skillet and cook until browned on both sides and cooked through, 4 to 6 minutes per side for medium-well.

Step 4

Assemble the burgers: Place the burgers on the buns, and layer with lettuce, red onions and tomatoes.