01 -
Divide ground chuck into six ⅓-pound portions and shape each into a loose ball. Place on a tray and refrigerate for 30 minutes.
02 -
Using a mandoline with proper hand protection, slice white onions as thinly as possible. Squeeze excess liquid from onions and refrigerate until ready to use.
03 -
Fry bacon strips until fully crisp. Drain on paper towels and chop finely. Reserve half for the baconnaise sauce and half for burger assembly.
04 -
In a bowl, combine mayonnaise, ketchup, mustard, Worcestershire sauce, apple cider vinegar, seasoning blend, red pepper flakes, and half of the chopped bacon. Stir thoroughly and refrigerate.
05 -
Preheat griddle over medium-high heat and coat with avocado oil. Place chilled beef balls on griddle with 2 inches between each. Add sliced onions on top of each ball. Using a spatula, smash each ball flat so onions press into the beef. Season with salt, pepper, and garlic.
06 -
Grill patties without moving for 3-4 minutes until a deep crust forms. Spread yellow mustard on the exposed side, then flip so onions are against the griddle. Top with pepper jack cheese and cook 3 more minutes until cheese melts and onions caramelize.
07 -
Place burger buns cut-side down on the griddle until golden and slightly crisp, about 1 minute.
08 -
Spread baconnaise sauce on bottom bun. Stack two smash patties with onions and cheese on top. Add more baconnaise and reserved chopped bacon, then cap with top bun.