Mix the sauce ingredients together in a small bowl.  Form the ground beef into 4 balls approximately ¼ pound each.

Preheat the blackstone grill over medium high heat (approximately 400 degrees F).

Melt the butter in one section of the grill.  Then top the melted butter with the chopped onions.  Sauté the onions in the butter until they are caramelized (3-5 minutes).

While the onions are cooking, drizzle the avocado oil over the other side of the grill.

Place the buns on the grill over the oil for 2 minutes to toast them and then set them aside while you prepare the beef.

Then place the beef balls on the grill. Then top each one with a piece on parchment paper and firmly press down to smash the beef into a thin patty with either a burger press or a large spatula and then discard the parchment paper.

Season the patties with salt and pepper.

Cook the patties for 2 minutes until the juices in the beef start to raise to the top and the color starts to change. While the patties are cooking, top each of the patties with 1 tablespoon of mustard on the raw side.  Then scrape under the patty to get under the caramelized parts and flip the patty.

Once flipped, do not smash down the patties again. Cook for 1 more minute and place 2 pieces of cheese on each of the patties.

Cook for 1 more minute to allow the cheese to melt.

Then it’s time to assemble your burgers.

Spread the sauce on the top and bottom of the bun. Then top the bottom bun with the lettuce, tomatoes, patty and sauté onions.  Then the top bun.

Then the burgers are ready to enjoy!