In a large skillet, melt 2 tablespoons of butter over medium heat. Add 2 sliced onions and cook, stirring frequently, until they turn a deep golden-brown color, approximately 10-12 minutes.

Once your onions are caramelized, push them to the side of the skillet and add 1 pound of ground beef to the center. Break the meat apart with a spatula and cook for about 5-7 minutes until browned and fully cooked.

Stir in 2 tablespoons of gluten-free soy sauce and any optional vegetables like diced mushrooms or bell peppers. Cook everything together for an additional 2-3 minutes.

Top each portion with slices of provolone or Swiss cheese. Cover the skillet with a lid and allow it to cook on low heat for about 1-2 minutes until the cheese melts.

Preheat your oven to 350°F (175°C). Split your buns in half and place them on a baking sheet. Toast them in the oven for about 5-7 minutes.

Remove the buns from the oven and spoon generous amounts of the beef mixture onto each bun.

Serve your French Onion Beef Sloppy Joes immediately, paired with sides of your choice.