Make the Secret Sauce: In a small bowl, mix together the mayonnaise, ketchup, Dijon mustard, garlic powder, onion powder, salt, and pepper. Set it aside.

Cook the Onions: In a skillet over medium heat, melt 1 tablespoon of butter. Add the sliced onions and cook until caramelized and golden brown, about 8-10 minutes.

Form the Patties: Season the ground beef with salt and pepper, then form it into two equal patties.

Sear the Patties: In the same skillet, add more butter if needed and cook the patties for about 3-4 minutes on each side until browned.

Assemble Your Melts: Spread a generous amount of secret sauce on one slice of bread, top with a patty, caramelized onions, and cheese. Top with another slice of bread.

Grill Time: Place your sandwiches in the skillet over medium heat. Cook for about 3-4 minutes on each side until the bread is golden and crispy and the cheese melts.

Serve and Enjoy: Slice the melts in half and serve with fries, pickles, or a light salad.