Combine all ingredients for Big Mac sauce. Let sit in the frige for a few hours, up to overnight. While chilling, stir once every few hours.
Ingredient Prep and Mise en Place
Remove lettuce and wash in ice cold water. Dry and set aside.
Cut the tomato into ½ inch slices.
Cut onion into thin slices. Place in an ice bath for 5-10 minutes to remove bite. Drain and set aside.
In a dry cast iron pan, toast the buns cut side down. Set aside and keep under a plate to keep warm while cooking the burger buns.
Burgers
If grinding own meat, take ¾lb of beef chuck and ¼lb of bacon and grind together. Mix until combined and set aside. Form into patties about 1 inch wider than the diameter of burger buns and line with parchment paper. Place in the fridge for 30 minutes.
When ready to cook, heat a cast iron skillet over high heat with either oil or bacon fat. Season the patties with salt and cook for 4 minutes on the first side. Before flipping, add 1 teaspoon of mustard on the raw side, and then flip. Place a slice of cheese on the burger to melt while the second side cooks - for an additional 2-3 minutes or until an instant read thermemoter reads 160 degrees.
Assembly
Take the bottom of the burger bun and line with a spoonful of Big Mac Sauce. Next, place the lettuce, tomato, onions followed by the burger and cheese. Top with pickles. Top the upper bun with a bit more sauce and serve with sides of choice.