- 1 cup blue cheese, crumbled
- 1/4 cup mayonnaise
- 2 teaspoons Dijon mustard
- 1 1/2 pounds 80% lean ground beef
- 1 teaspoon salt, plus more to taste
- 1 teaspoon ground black pepper, plus more to taste
- 4 hamburger rolls, split
- 2 cups mixed greens, loosely packed
- 2 thin slices red onion, separated into rings
- 16-20 basil leaves
- Combine the cheese, mayonnaise, and mustard in a small bowl; add salt and pepper to taste and set aside.
- Gently shape the beef into four patties about 3/4-inch thick. Sprinkle with the salt and pepper.
- Heat a large nonstick skillet or a grill pan over medium heat until hot. Cook the patties to desired doneness, about 3 1/2 minutes per side for medium-rare.
- Set the patties aside to rest. Meanwhile, place the buns cut side down in the skillet or grill pan to slightly toast them, about 1 minute.
- Place the bun bottoms on plates or a platter. Top with the mixed greens, patties, onion, cheese mixture, basil, and bun tops and serve.