Cheesy Burgers with Apple
- 3/4 pound 90% lean ground beef
- 1/3 cup finely chopped red onion
- 2 ounces sharp cheddar, cut into 1/4-inch cubes
- 1 tablespoon Dijon mustard
- 1/2 teaspoon fine sea salt
- 1/4 teaspoon freshly ground black pepper
- 1/2 cup shredded peeled Granny Smith apple
- 4 hamburger buns