2 bacon strips, sliced crosswise into ½-inch pieces

1½ teaspoons caraway seeds

2 tablespoons unsalted butter, divided

1 medium yellow onion, halved and thinly sliced lengthwise

2¼ teaspoons kosher salt, divided

¾ pound 85% lean ground beef

1 tablespoon Worcestershire sauce

2 teaspoons Dijon mustard

½ teaspoon freshly ground black pepper

¼ teaspoon garlic powder

2 tablespoons mayonnaise

4 slices rye bread

4 slices Swiss cheese