1Caramelize onions in butter until golden brown, season with salt.
2Mix mayonnaise into minced beef for extra juicy patties. Season with salt, pepper, and garlic powder. Add mustard, mix well. Form into patties and cook in a pan with oil until cooked to desired doneness.
3Make the secret sauce by combining ingredients in a bowl.
4Assemble burgers with toasted buns, cheese, lettuce, tomato, caramelized onion, and secret sauce.
5Cook French fries until golden brown. Top with secret sauce, caramelized onions, and cheese.