1 ½ lb. 80% lean ground beef
Kosher salt and coarse black pepper
¼ cup Worcestershire sauce
1 tsp. ground white pepper
About 1/4 tsp. freshly grated nutmeg
1 small to medium white onion, very thinly sliced with a sharp knife or a mandoline
½ cup distilled white vinegar
2 tsp. sugar
1 tbsp. olive or canola oil
8 slices Swiss cheese
1 jar or pouch (16 oz.) sauerkraut
1 tsp. each caraway seeds and cumin seeds
4 pretzel rolls, split
Brown mustard, for spreading
Dill pickle chips, for topping
Preheat the oven or toaster oven to 350°. In a medium bowl, season the beef liberally with kosher salt and black pepper. Mix in the Worcestershire, white pepper, and nutmeg. Form into 4 patties (thinner in the centers for even cooking).
Place the onion in a small bowl. In a small saucepan, bring the vinegar, sugar, and 1 tsp. salt to a simmer over medium heat, stirring until the sugar and salt dissolve, 1 to 2 minutes. Pour the vinegar over the onions and let cool. Drain the onions before using.
Heat a large cast-iron skillet over medium-high. Add the oil, one turn of the pan. Add the patties. Cook for 8 minutes, turning occasionally. During the last minute or two of cooking, top each patty with 2 slices of cheese. Tent the skillet loosely with foil to melt the cheese
In a small saucepan, heat the sauerkraut, caraway seeds, and cumin seeds over medium until heated through, 3 to 4 minutes.
Warm the rolls in the oven until heated through, about 2 minutes.
Spread the roll bottoms with the mustard. Top with the pickle chips, pickled onions, cheeseburgers, sauerkraut, and roll tops.