1 lb (450 g) ground beef Salt to taste Freshly ground black pepper to taste 1 large onion, thinly sliced 4–6 slices Swiss cheese 8 slices rye bread 3 tbsp (45 ml) unsalted butter 1 tsp (5 ml) Worcestershire sauce (optional)
1. Heat 1 tbsp butter in a skillet over medium; add onions and a pinch of salt and cook, stirring occasionally, until deeply caramelized (15–20 minutes). Stir in Worcestershire if using. Transfer onions to a bowl. 2. Form four thin patties, season with salt and pepper, and cook in the same skillet 2–3 minutes per side until just done. Remove. 3. Build sandwiches: place a patty on a slice of rye, top with caramelized onions and Swiss, then another rye slice. 4. Butter outer sides of each sandwich and return to the skillet over medium heat. Grill 3–4 minutes per side until bread is golden and cheese is melted. 5. Slice in half and serve hot.
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