Heat grill to high heat (about 450°F).
On a cutting board, stack 4 slices of Cooper Sharp cheese. Cut into small pieces, approximately 1 1/2 by 2 1/2 inches, to form 2 stacks of cheese (you’ll have some bits of cheese left over—feel free to snack on them, we won’t tell). Freeze the 2 stacks for approximately 15 minutes. Set the remaining 4 slices of Cooper Cheese in the refrigerator until ready to use.
In a medium bowl, mix ground beef with chopped onion, Worcestershire sauce, salt and pepper. Divide mixture into 4 sections and form into patties (about 4 ounces each). Set patties on a plate. Layer 1 stack of frozen Cooper Cheese on each patty. Set a second patty on top of each and pinch around the edges to seal the cheese inside.
Place the patties on the grill and cover, either with grill lid, grilling dome or stainless steel bowl. Grill until marks appear in the patties, or about 3 minutes.
Carefully uncover the patties and flip (grill cover will be hot). Close the cover and grill for another 3 minutes. Carefully remove the cover and layer 2 slices of Cooper Cheese, crisscrossed, on top of each burger. Cook until cheese is melted (covering again will speed up the melting process). Remove patties from grill and let burgers rest for 5 minutes.
Build your burgers using your favorite bun and burger toppings such as tomatoes, lettuce, pickles and condiments.
This recipe can also be made on a stovetop and finished in the oven. Preheat oven to 400°F. Once stuffed burger patties are formed, preheat an oven-safe skillet to medium high. Add 1 tablespoon olive or corn oil. Carefully place burger patties into the skillet to sear for 2 minutes per side. Then place skillet in the oven for 5 minutes, or until desired doneness. Remove skillet and rest burgers on a cutting board. Add more Cooper Cheese if desired and assemble the burgers along with your favorite burger toppings.