You will need 1 tablespoon of olive oil.
2 cups chopped onion from 1 large onion
6 tablespoons unsalted butter, divided garlic powder, kosher salt
2 tablespoons ketchup
1.5 pounds lean ground beef
2:1 Worcestershire sauce
8 slices rye bread
Onion powder; 1/2 teaspoon
Swiss cheese, sliced approximately 250 grams
Directions:
Heat the olive oil in a large skillet over medium-low heat. Add the sliced onions and fry, turning regularly, until golden brown and caramelized, 20 to 25 minutes. Season with salt and pepper. While waiting, heat a cast iron skillet over medium heat. Melt 2 tablespoons of butter in a hot frying pan.
In a large bowl, carefully combine ground beef, ketchup, Worcestershire sauce, 1/2 teaspoon onion powder, 1 teaspoon salt, and a pinch of pepper. Form 4 equally sized meatballs from the meat mixture. Roll out each piece into a circle slightly wider than a loaf of bread. Fry the patties in a hot frying pan for 4-5 minutes on each side until golden brown. Remove from the pan and set aside.
Wait until the patty is melted. Remove excess fat from skillet and melt remaining 2 tablespoons butter in medium saucepan. Place 4 slices of rye bread, buttered side down, in the pan. Place a burger patty, Swiss cheese, half of the caramelized onion, and a second piece of cheese on each bun. Place the melted bread slices, buttered side up, along with the other 4 slices of buttered bread.
Recommended cooking time for each patty is 2 to 4 minutes per side, until golden brown and melted. Occasionally press down on the cheese with a spatula.