Begin by dividing the ground chuck into 1/3 pound portions and gently roll them into balls. Refrigerate for about 30 minutes.

Using a mandoline, thinly slice the white onions and squeeze out excess moisture with a clean towel.

Cook the bacon in a skillet over medium heat until crispy, about 8-10 minutes. Chop into small pieces after cooking.

In a medium bowl, mix mayo, ketchup, mustard, chopped bacon, Worcestershire sauce, apple cider vinegar, all-purpose rub, and red pepper flakes until well-blended.

Preheat griddle or skillet to medium-high heat for 5 minutes and drizzle with avocado oil.

Place chilled burger balls on the griddle, add sliced onions, and smash with a burger press.

Season with salt, pepper, and garlic during the last minute of cooking; add mustard and cheese after flipping.

Toast burger buns cut-side down on the griddle for 1-2 minutes until golden brown.

Assemble by spreading Baconnaise sauce on the bottom bun, placing the burger, adding more sauce, and topping with the bun.

Serve immediately with your favorite sides.