Grilled cheese-stuffed burgers

Ingredients:

• 0.7 kg ground beef
• 110 g cheddar, cut into 16 small cubes
• 1/3 cup ketchup
• 2 tablespoons Worcestershire sauce
• 4 sesame seed burger buns, split in half horizontally and toasted
• 4 small romaine lettuce leaves
• 4 slices sweet onion
• 1 small ripe tomato, cut into 4 slices
• Potato chips or French fries, for serving

Preparation:

1. Preheat the grill to high heat. Form the ground meat into 4 balls, weighing 180g (625g). Press 4 small cubes of cheese into the center of each ball and form them into 1/2-inch-thick, 4-inch-diameter patties, ensuring the cheese stays inside the ground meat. Sprinkle both sides of the patties evenly with 1 teaspoon of salt and 1/2 teaspoon of black pepper. Wrap each patty in a piece of nonstick aluminum foil, twisting the excess foil at each end so that the patty is wrapped in only one layer. Combine the ketchup and Worcestershire sauce in a small bowl.
2. Grill the patties for 5 minutes per side. Remove from the grill and carefully unwrap the foil packages to release steam. Return the open packages to the grill, spoon a spoonful of sauce onto each patty, and continue cooking until the patties are at least medium-rare and the cheese is completely melted, another 4 to 6 minutes.
3. Spread a little sauce on the bottom half of each bun, top with a lettuce leaf, an onion slice, and a tomato slice. Place a patty on top, add another spoonful of the remaining sauce, and top with the remaining bun halves. Serve the burgers with chips or fries.