Preheat the Blackstone Grill over medium high heat (approximately 450 degrees F).  Divide the ground beef into 2 even balls (approximately 3 oz each).

Butter one side of each piece of the sourdough bread with 1 Tbsp of the butter.

Melt the remaining butter on one side of the griddle.  Then top the melted butter with the sliced onions.  Sauté the onions in the butter until they are caramelized (3-5 minutes).

While the onions are cooking, place the ground beef on the grill.  Put a piece of parchment paper on top of the beef and use a spatula or a burger press to smash the meat into 2 thin patties.

Let the patties cook until they are browned and crispy (2-3 minutes).  Then flip the patties over (do not smash) and cook the other side for 2-3 minutes until it is also browned and crispy.

Place a piece of the Swiss cheese on each patty.

Put the bread on the blackstone grill butter side down and toast the bread.

Then assemble the sandwich.  Place one piece of the bread on a plate (toasted side down), top with 1 of the patties, half of the fried onions, then the remaining patty, the rest of the fried onions and top with the 2nd piece of bread (toasted side on top).

Cut in half and the patty melt is ready to serve and enjoy!