Aunt Sheila would slide these onto the table and somehow they’d disappear before the sweet tea even hit the glasses.

Preheat your oven to 400°F (200°C). Line 2 large rimmed sheet pans with foil for easier cleanup and lightly coat them with nonstick cooking spray.

Season the ground beef in a large bowl with 1 1/2 teaspoons kosher salt, 1 teaspoon black pepper, garlic powder, onion powder, smoked paprika, and Worcestershire sauce. Use your hands or a fork to gently mix until the seasonings are evenly distributed, being careful not to overwork the meat.

Divide the seasoned beef into 8 equal portions and shape each portion into a thin, rectangular patty roughly the size and shape of your bread slices. Lay the patties on one of the prepared sheet pans, leaving a little space between them.

Bake the patties on the center rack for 10 to 12 minutes, or until just cooked through and no longer pink in the center. They will cook a bit more later in the sandwiches, so avoid overbaking. Remove from the oven and set aside, keeping the oven on.

While the patties bake, heat the vegetable oil and 2 tablespoons of the butter in a large skillet over medium heat. Add the sliced onions and 1/2 teaspoon kosher salt. Cook, stirring often, until the onions are soft, golden, and lightly caramelized, 15 to 20 minutes. If they start to brown too quickly, lower the heat and add a splash of water to loosen any browned bits.

In a small bowl, stir together the mayonnaise and mustard to make a quick spread. Taste and adjust the ratio to your preference—more mustard for tang, more mayo for richness.

Lay the 16 slices of bread out on the second prepared sheet pan and any open space on the first pan. Lightly spread one side of each slice with the mayo-mustard mixture, going all the way to the edges. This side will face inward toward the filling.

Flip each bread slice so the spread side is facing up. Place a slice of Swiss cheese on 8 of the slices. Top each cheese-covered slice with a warm beef patty, then a generous spoonful of caramelized onions. Add a second slice of Swiss over the onions if you like things extra cheesy.

Top each stack with a second slice of bread, spread side facing down toward the filling, to form 8 sandwiches. Gently press each sandwich so it holds together.

Melt the remaining 1 tablespoon of butter. Lightly brush or dab the tops of the sandwiches with melted butter. If you prefer, you can skip the extra butter and simply spray the tops very lightly with cooking spray for browning.

Return the sheet pans to the oven and bake the sandwiches at 400°F (200°C) for 8 to 10 minutes, flipping once halfway through if you want both sides deeply toasted. The bread should be golden and crisp, and the cheese fully melted.

Transfer the hot patty melts to a paper-lined plate or directly to serving plates. Cut each sandwich in half on the diagonal if desired. Serve immediately with extra Thousand Island or Russian dressing on the side for dipping, plus pickles and your favorite Southern sides. Expect them to disappear before the sweet tea even hits the glasses.

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