8 slices bacon, crisply cooked, drippings reserved
2 large sweet onions, thinly sliced (about 1 1/2 lb)
1 bottle (12 oz) pilsner style beer
1 1/2 lb lean (at least 80%) ground beef
1/2 teaspoon salt
1/4 teaspoon pepper
4 slices (about 3/4 oz each) Cheddar or American cheese
8 leaves red leaf lettuce or red romaine lettuce
4 slices tomato
4 kaiser rolls or crusty rolls, split
1. In 10-inch skillet, heat 1 tablespoon bacon drippings over medium-high heat. Add onions; cook about 15 minutes, stirring frequently, until softened.
2. Reserve 1/2 cup of the beer. Stir remaining beer into onions. Heat to boiling; reduce heat to medium and simmer uncovered, stirring occasionally, until onions are golden and liquid has evaporated, about 30 minutes. Cool.
3. Meanwhile, roughly chop 4 slices of the cooked bacon; set aside. Roughly chop half of the onion mixture; stir into chopped bacon.
4. In medium bowl, stir chopped onion and bacon mixture into beef. Add salt and pepper. Shape beef mixture into 4 large patties, thinner at center and thicker at edges for even cooking.
5. In 10-inch skillet, heat remaining bacon drippings over medium-high heat. Add patties; cook 8 minutes for medium-rare, 10 minutes for medium, 12 minutes for medium-well, turning once. After turning, add reserved 1/2 cup beer to burgers, then top burgers with cheese. Cover skillet to melt cheese.
6. Place burgers on bun bottoms; top with lettuce leaves, tomato slices, and remaining caramelized onions. Cut remaining 4 slices bacon in half; crisscross 2 pieces on top of onions on each burger, and cover with tops of buns.