2 tablespoons extra-virgin olive oil
1 tablespoon unsalted butter
1 teaspoon kosher salt
4 tablespoons balsamic vinegar, divided
3 large yellow onions, sliced into rings
1 pound ground sirloin
¼ teaspoon kosher salt
¼ teaspoon ground black pepper
8 slices of fresh rye bread, toasted
8 large slices of Swiss cheese, or a combination of Swiss and American
In a large heavy-bottomed saute pan or Dutch oven over medium heat, combine the olive oil and butter. When the butter is melted, add the salt, 3 tablespoons of the vinegar, and the onion rings. Cover and cook for 20 minutes, stirring occasionally.
Remove the cover and cook, stirring occasionally, for another 10 minutes, or until the onions are all a deep golden color. When the onions are done, transfer them to a bowl and immediately drizzle the remaining vinegar over them. Stir to combine, then set aside. The onions can be prepared to this point up to 2 days ahead, then refrigerated in an airtight container.
When ready to cook the burgers, prepare a grill for direct, medium heat cooking.
Being careful not to overwork the meat, season the sirloin with salt and pepper, and mix until combined. Gently shape the meat into 4 oval patties of equal size and thickness (about ⅓ inch thick).
Use your thumb to make an imprint in the center of each patty. Place each patty directly on the cooking grate and grill for 4 minutes. Turn and continue grilling until the meat is no longer pink, another 4 to 5 minutes. Once the patties are made and grilled, transfer to a clean platter.
Meanwhile, begin to assemble the patty melts by layering each piece of the rye toast with a slice of cheese. Take the bread to the grill and place directly on clean cooking grates for 1 to 2 minutes, or until the cheese begins to melt and the bread is warm and lightly toasted.
Once the cheese has melted, transfer each burger patty to one slice of bread. Divide the onions between the remaining 4 slices of bread, then assemble into 4 sandwiches.
Nutrition values per serving: 720 calories, 44 g fat (17 g saturated; 1 g trans fats), 41 g carbohydrates, 4 g fiber, 9 g sugar, 46 g protein, 140 mg cholesterol, 1,140 mg sodium.
Elizabeth Karmel for The Associated Press