In a large skillet, melt 2 tablespoons of butter over medium heat. Add thinly sliced onions, stirring frequently, and let them sauté for about 10-15 minutes until they turn a deep golden brown.

Once the onions are caramelized, push them to the side and add 1 pound of ground beef to the skillet. Break the beef apart and cook for about 6-8 minutes until browned. Drain excess fat.

Stir the caramelized onions back into the skillet with the browned beef. Add 2 tablespoons of gluten-free soy sauce and mix well. Optional: add any add-ins and let simmer on low for another 3-5 minutes.

Preheat your oven broiler and lightly toast the buns. Spoon generous portions of the beef and onion mixture onto each bun.

Top each sandwich with a slice of cheese and place under the broiler for 2-3 minutes until the cheese bubbles and is golden.

Serve immediately, perhaps with a side of oven-baked fries or a fresh salad.