In a large mixing bowl, combine ground beef, egg, Worcestershire sauce, brown mustard, and unsalted butter. Add bread crumbs, grated Parmesan cheese, minced garlic, and fried onions if desired. Mix gently until just combined.

Divide the mixture into four equal portions and shape each into a uniform patty, about ¾-inch thick, making a slight indentation in the center.

Sprinkle seasoning evenly over the patties before cooking. Let rest for about 10 minutes.

Preheat your grill to medium-high heat, around 400°F (200°C).

Grill the patties for about 4-5 minutes per side until a char forms and a meat thermometer reads 160°F (71°C). Add cheese on top during the last minute if desired.

Remove burgers from the grill and let rest for a couple of minutes. Serve on toasted buns with toppings of choice.