Add 1 tbsp butter to heavy pan (cast iron preferred) and preheat over medium-low heat
Cook the onion and jalapeno slices until caramelized, about 20 minutes
While the vegetables are cooking, make the sauce: combine all ingredients in a bowl, mix to combine, and set aside.
When the onion and jalapeno slices are almost done, divide the hamburgers into 2 5-oz balls, flatten, and season one side with salt, pepper, and garlic powder
When the vegetables are done, remove from the pan, turn the heat to medium high, and add 1 hamburger, seasoned side down, season the top with more salt, pepper, and garlic powder. Cook burger until edges are brown on top, about 5 minutes, then flip and cook until done, about 3-4 minutes
While the hamburger is cooking, take 2 slices of bread, slather the sauce on one side of each, add the American cheese to one slice and the Swiss cheese to the other slice, and place half of the vegetable slices on top of the American cheese.
When the hamburger is done, add it on top of the vegetables, and add the other slice of bread on top to build the burger. Wipe the plan clean and add 1/2 tbsp butter and melt. Place the assembled burger in the pan and cook like a grilled cheese until golden brown, about 3 minutes. Add another 1/2 tbsp butter, flip, and cook the other side.
Remove from pan, slice diagonally, and repeat for the other burger.
Notes
For some additional heat, add some cayenne pepper to the sauce.
Nutrition
Calories: 850kcal
Keyword burger, cheese, diner, jalapenos, late night, onions, patty melt