For the burgers:
1 lb. ground sirloin
2 tbsp. finely chopped yellow onion
1 clove garlic, minced
1 tsp. salt
½ tsp. pepper
1-2 dashes Worcestershire sauce
For the topping:
4 slices of bacon or pancetta, chopped
2 cups white or cremini mushrooms
2 large garlic cloves, minced
1 tbsp. minced shallot
1 tbsp. tomato paste
1 ½ cups Marsala wine (sweet)
1 ½ tbsp. fresh lemon juice (1 small lemon)
3 tbsp. unsalted butter, cut into pieces, at room temperature
Sliced provolone cheese, for serving
Hamburger buns, for serving
Heat the grill to medium-high. To prepare the burger patties, combine the ground sirloin, onion, garlic, salt, pepper and Worcestershire sauce in a medium bowl. Mix together until well combined. Form into 4 equal sized patties. Refrigerate until ready to use.
To make the topping, place a skillet over medium heat. Add the pancetta to the pan; sauté, stirring occasionally until pancetta is brown and crisp, about 4 minutes. With a slotted spoon, transfer the pancetta to a paper-towel lined plate. Add mushrooms and increase heat to medium-high; sauté, stirring occasionally and scraping pan bottom, until liquid released by mushrooms evaporates and mushrooms begin to brown, about 8 minutes. Add garlic and shallot; sauté for 1 minute.
Return the cooked pancetta to the pan and add the tomato paste. Stir while sautéing, until tomato paste begins to brown, about 1 minute. Off heat, add Marsala; return pan to high heat and simmer vigorously, scraping browned bits from pan bottom until sauce is slightly syrupy and reduced to about 1 ¼ cups, about 5 minutes. Stir in the lemon juice. Whisk in the butter until completely melted. Keep the sauce warm over low heat while grilling the burgers.
Grill the burgers, 3-5 minutes per side, until cooked through and no longer pink (160˚ F on an instant read thermometer). Place a slice of provolone on top of each patty during the last few minutes of cooking. Toast the burger buns on the grill until light golden. Assemble the burgers on the buns and spoon the Marsala topping over the patties. Serve immediately.