In-N-Out Double Double - Animal Style (Copycat)

1. Form meat into four 2 ounce patties, thin and slightly larger than the size of your bun. They are meant to be a 1/4 inch thick.
2. Heat 1 tablespoon butter in a skillet over medium-high heat until shimmering.
3. Add onions and 1/2 teaspoon kosher salt to skillet.
4. Reduce heat to medium low, and cook, tossing and stirring occasionally until onions are well browned, about 15 minutes.
5. Preheat oven to 400 degrees.
6. Once onions begin to sizzle heavily and appear dry, add 1 tablespoon water to skillet and stir.
7. Continue cooking until water evaporates and onions start sizzling again.
8. Repeat process, adding 1 tablespoon of water with each iteration until onions are meltingly soft and dark brown, about 3 times total.
9. Transfer to a small bowl and set aside while leaving any residual butter in the pan.
10. To make the burger and animal fry topping: Add mayonnaise, ketchup, relish, sugar, and vinegar to a small bowl and stir to combine.
11. Place closed buns in preheated oven for 2 minutes until slightly darker and just the slightest bit crispy.
12. Using the butter left behind by the onions, press the buns into the pan and toast for a few seconds until crispy.
13. If there is no butter left in the pan, add a 1/2 a tablespoon or so to the pan.
14. Season the patties with salt and pepper.
15. Preheat pan on high and add the patties to the pan.
16. Cook without moving until well browned and crusty on first side, about 2 1/2 minutes.
17. While they are cooking, spread about a tablespoon of mustard to the raw side.
18. Flip and cook the mustard side as well, another minute.
19. Add the sauce to each half of the bun.

From the bottom up:

1. Add four pickles, then one slice of tomato and lettuce.
2. Top each meat patty with a slice of cheese and half the caramelized onions.
3. Stack two patties together and add on top of the lettuce.
4. Top with top bun.