• Season the beef. In a mixing bowl, combine the ground beef and the ground sirloin. Sprinkle in the salt, pepper, garlic powder, onion powder, and Worcestershire sauce. Gently mix by hand until just combined. Don't overmix! This is how you end up with tough and dry burgers.
• Shape the patties. Divide the ground beef mixture into 4 equal portions (about 6 oz each). Use a burger mold to firmly press the burgers into patties. Transfer the formed patties to a parchment lined baking sheet and refrigerate the burgers for 30 minutes.
• Make the burger sauce. In a small mixing bowl, add all the ingredients for the burger sauce and mix well. Season to taste with salt and pepper and refrigerate until ready to use.
• Prep the grill for zone cooking. Light one side of the grill over medium heat. Close the lid and preheat for 10-15 minutes. Make sure the grates of your grill are cleaned of any debris and lightly grease them with oil or nonstick cooking spray.
• Grill the burgers. Season the outside of the burger patties with salt and pepper. Place the burgers over direct heat and grill for 3 minutes per side, just until grill marks form with the lid open. Turn off the heat and move the burgers to the side of the grill that was not lit and close the lid for 5 minutes. Place the cheese slices on top of the burgers and close the lid for 1 more minute.
• Assemble the burgers. Remove the burgers from the grill and let them rest for 5 minutes. Assemble them on the toasted buns with burger sauce, lettuce, tomato, and onion. Enjoy right away.

Alternative Cooking Methods

• To cook in a cast iron skillet: Add 2 tablespoons of neutral oil to the bottom of a 12-inch cast iron skillet over medium heat (enough so that it coats the surface). Heat until a drop of water sizzles when dropped into the pan. Gently add the burgers into the pan and cook for 4 minutes. Carefully flip the burgers, and cook for another 4 minutes. Top with cheese and let the cheese melt onto the burgers. Remove the burgers from the pan and let them rest for 5 minutes.
• To cook on a stovetop grill pan: Preheat your grill pan over medium heat for at least 5 minutes. Lightly drizzle a bit of neutral oil over the pan. Once the oil is hot, add the burgers to the pan and cook them for 4 minutes per side, until cooked to desired doneness. Remove the burgers from the pan and let them rest for 5 minutes.

Storage & Make Ahead Options

• Storage and make-ahead option: Patties may be formed up to 24 hours before cooking. Store in a covered container in the fridge. After cooking through, store in an airtight container in the fridge for up to 4 days.

  To reheat: Reheat the burgers by warming incrementally in the microwave until warmed through. Alternately warm them in a skillet with a lid over low heat until warmed through.