Heat the grill to medium-high heat.
To make the burger sauce: In a small bowl, combine all of the ingredients together until well incorporated. Set aside.
To make the burgers: Use a kitchen scale to measure out 6 ⅓-pound balls of ground beef, and then form them into 3/4-inch thick patties. Make a thumb indent in each patty. The indent will help the patty hold its shape as it cooks, rather than swelling — and that will help it cook more evenly.
Generously season both sides of the patties with salt and pepper.
Place the patties on the hot grill and cook, covered, for 5 to 7 minutes. Flip the patties and cook them for another 5 minutes.
Top each patty with 3 half strips of bacon and 2 slices cheddar, and cook the patties, covered, for 1 to 2 minutes, or until the cheese is melted.
Remove the patties and set them aside to rest for 5 minutes.
Meanwhile, toast the buns on the grill for 2 minutes, or until they’re golden and have nice grill marks.
Top each of the warm buns with a burger patty, burger sauce, lettuce, tomato and onion.