Cast-Iron Burgers

These premium cast-iron burgers prove that you don't have to own a grill to enjoy juicy, surprisingly flavorful burgers.
To make the patties, divide the beef into 4 portions, lightly shaping each into a 1/2-inch thick patty. Sprinkle evenly with salt. Cover and refrigerate for 30 minutes.To make the horseradish spread, combine the mayonnaise and the following 3 ingredients (with ketchup added) in a small bowl. Set aside.To make the savory sauce, saute the bacon in a large nonstick skillet over medium-low heat until crisp. Use a slotted spoon to remove the bacon from the pan. Add the onion to the filling in the pan; cook for 15 minutes or until golden brown. Combine the bacon, onion mixture, spring onions, Worcestershire sauce and pepper in a small bowl.Heat a large cast-iron skillet over medium-high heat. Brush the mold with cooking spray. Add the meatballs; cook for 2 minutes on each side or until just cooked through. Spread 1 1/2 teaspoons horseradish on the cut sides of each bun half. Place on the bottom half of each bun 1 patty, 1/4 cup sauce, 1 slice of tomato, 1/4 cup lettuce leaves, and the top half of the bun.