Divide the ground beef into 2 even balls (approximately 3 oz each) and butter one side of each piece of the Rye bread with 1 Tbsp of the butter.
Melt the remaining butter in a large skillet (or cast iron pan) over medium high heat. Then top the melted butter with the sliced onions. Sauté the onions in the butter until they are caramelized (3-5 minutes). Remove the onions from the skillet and set aside.
Place the ground beef on the skillet over medium high heat. 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 and allow it to melt. Then remove the patties from the skillet and set aside.
Put the bread on the skillet 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!
Notes
You can easily use any of your favorite types of cheese in this recipe if you do not like Swiss Cheese. You can use sourdough or artisan bread if you prefer, but Freddies does use Rye Bread in their recipe. These patty melts are best served fresh.