Here’s your blueprint for a crowd-pleasing backyard barbecue burger complete with special sauce. The sauce is no secret here: Crunchy iceberg lettuce and pickles provide crunch and tang, all mixed in with ketchup, mustard, and a little hot sauce for kick. We like the texture whole-grain mustard adds to the sauce, but creamy Dijon will work just as well. Don’t overwork the beef as you form the patties so the burgers stay moist and juicy.
Preheat grill to medium-high (about 450°F). Combine first 5 ingredients in a small bowl.
Gently shape ground sirloin into 4 (4-inch-wide) patties. Sprinkle evenly with salt and pepper. Coat grill grate with cooking spray. Place patties on grate; grill 4 minutes on each side or to desired degree of doneness.
Place 1 lettuce leaf on bottom half of each bun. Top each with about 2 1/2 tablespoons sauce, 1 patty, 1 tomato slice, and 1 onion ring. Cover with top halves of buns.