Cooking Instructions

• In a large cast-iron skillet set over medium heat, add 1 tablespoon of butter and sliced onions. Cook for about 25 minutes until deep brown, then add apple cider vinegar and remove from skillet.
• Shape ground beef into two thin 4-ounce patties, season with salt and pepper, and cook in the skillet over medium-high heat for 3 minutes per side. Remove when done.
• Wipe the skillet clean, melt the last tablespoon of butter, and add all the bread slices, buttering one side. Remove two slices and start building the sandwiches on the two remaining in the skillet.
• On each slice in the skillet, add a slice of Swiss cheese, a patty, half of the caramelized onions, and another slice of Swiss cheese. Top with the removed slice, buttered side up.
• Cook sandwiches over medium-low heat for 3 to 4 minutes per side until the bread is toasted and the cheese is melted.
• Slice sandwiches in half and serve immediately while warm.