Step 1

Preheat the grill.

Step 2

To make the jam:

Step 3

Heat the olive oil in a skillet over medium heat. Add the onions and sauté until they begin to turn golden and soften. Add a few tablespoons of water and cook until evaporated. Add 1 tablespoon of vinegar and stir to avoid sticking. Add the remaining water and cook until evaporated. Add the remaining vinegar, 1/2 teaspoon salt and 1/2 teaspoon pepper. Cook until evaporated, stirring constantly. Turn off the heat and set aside. (The mixture should be soft and broken down, like a lumpy jam.)

Step 4

To make the patties:

Step 5

Divide the beef into 12 equal pieces and form into patties approximately 1/4 inch thick. Place the cheese cubes on the center of six of the patties and place the remaining patties on top. Pinch the sides to form a tight seal.

Step 6

Grill the burgers over medium heat for 3-4 minutes. Turn the burgers over and cook an additional 3 minutes or until done.

Step 7

Place the burgers on the roll with lettuce, if desired, and top with the jam. Place the top of the roll on the burger and serve immediately.