Roasted Mushroom and Cheddar Stuffed Burgers

Warning: this method creates incredibly juicy burgers. You'll probably want to use a fairly substantial bun for them! If you don't want to do the filling here, just skip the initial step and create the undivided patties. I scaled the recipe down, but have included the original below which cooks enough for 6.

Roasted Mushroom and Cheddar Stuffed Burgers (from All About Roasting)

Ingredients
2 tbsp unsalted butter
225g button mushrooms, finely chopped
kosher salt and freshly ground black pepper
1 garlic clove, minced
1/4 cup chopped fresh parsley (I used cilantro instead)
1/4 cup grated cheddar cheese (35g)
burger mix
1 1/2 tsp kosher salt
900g ground beef
1 tbsp Worcestershire sauce
1/2 tsp freshly ground black pepper

1. Preheat oven to 475. Line a rimmed baking sheet with aluminum foil, spread a thin layer of salt over foil to absorb drippings and prevent smoking. Arrange a wire rack so that it sits at least 3/4" above the surface of the pan.
2. Melt butter in a 12" skillet over medium heat. Add mushrooms, season, and increase heat to medium high. Saute until mushrooms release liquid and start to brown, about 4 minutes. Stir in garlic and parsley. Remove from heat and cool. When cooled, stir in cheese.
3. Break beef into 1 - 2" lumps with your hands and drop in a mixing bowl. Season with salt, Worcestershire, and pepper. Mix gently. Try to avoid overhandling.
4. Divide hamburger meat into 12 even portions. Shape into a thin 4" patty.
5. Divide filling among 6 of the flat patties. Top each patty with another flat patty and pinch edges and round the burger to make 6 burgers.
6. Roast burgers on the wire rack for 10 - 16 minutes, depending on desired level of doneness.