Instructions:
Step 1
Heat olive oil in a large pan over medium-low heat.
Step 2
Cook the sliced onions for 20-25 minutes, stirring regularly, until they caramelize to a deep brown color.
Step 3
Season with a pinch of salt and pepper to taste.
Step 4
Meanwhile, heat a cast-iron skillet over medium-high heat.
Step 5
Melt 2 tablespoons of butter in the skillet.
Step 6
In a large bowl, mix together the ground beef, ketchup, Worcestershire sauce, onion powder, 1 teaspoon of salt, and a pinch of pepper.
Step 7
Form the mixture into four equal patties slightly larger than the bread slices.
Step 8
Cook the patties in the heated skillet for 4-5 minutes on each side, or until well browned. Remove from the skillet and set aside.
Step 9
Prepare the patty melts: Remove any excess grease from the skillet and melt 2 tablespoons of the remaining butter in a medium saucepan.
Step 10
Place 4 slices of rye bread in the pan, buttered side down. Top each bread slice with a burger patty, Swiss cheese, half of the caramelized onions, and another slice of cheese.
Step 11
Finish with the remaining 4 slices of bread, buttered side up.
Step 12
Cook each patty melt for 2-4 minutes on each side, using a spatula to gently press down on the cheese occasionally, until golden brown and the cheese is melted.
Step 13
Once the patty melts are cooked, transfer them to a cutting board and slice diagonally. Serve and enjoy!