· 11/2 pounds ground beef
· 1 large red onion, peeled and sliced into ¼ inch rounds
· 2 tablespoons olive oil
· 2 tablespoons balsamic vinegar
· ½ cup mayonnaise
· 1 bunch chives, sliced thin
· 1 clove garlic, finely minced
· 6 ounces blue cheese, crumbled
· Salt and black pepper
· Sliced tomatoes and baby spinach for garnish
· 4 Hamburger buns
Coat the sliced red onion with the balsamic vinegar and olive oil, sprinkle with salt and black pepper and marinate for about 1 hour.
Mix the chives, garlic, and mayonnaise together and reserve for use later.
Preheat a grill or cast iron griddle pan over medium high heat.
Form the ground beef into 4 - 6 ounce patties about 5 inches in diameter.
Grill the onion slices on the preheated grill for 2 to 3 minutes per side, or until well marked and just tender, remove and reserve someplace warm.
Season both sides of the hamburger patties with salt and black pepper and lightly coat with olive oil. Place the patties on the preheated grill and cook about 3 minutes per side for medium or until desired temperature. When the burgers are nearly done, distribute the crumbled blue cheese evenly over the 4 patties so the cheese warms and begins to melt. Remove the patties and reserve.
To assemble; slather a liberal amount of the chive aioli over the bottom piece of each bun, then the finished burgers, grilled onions, and optional tomatoes and baby spinach, serve immediately.