01 -
Shape 1/3 lb balls from the ground meat. Place in the fridge for 30 minutes.
02 -
Slice the onions thin using a mandoline. Squeeze out any liquid and pop them in the fridge.
03 -
Cook the bacon until crunchy, chop it, and set aside.
04 -
Stir together mayo, mustard, ketchup, a bit of bacon, Worcestershire, vinegar, seasoning mix, and chili flakes. Keep it cold.
05 -
Warm the griddle, lightly oil it, press the meat balls, top with onion slices, and smash into the griddle. Sprinkle on seasoning and let them cook 3–4 minutes.
06 -
Spread mustard on the top, flip the patties, toss on cheese slices, and cook another 3 minutes until melty.
07 -
Toast those buns, add a spread of sauce, layer up the double patties, drizzle more sauce, then finish with the top bun.