In a bowl, gently mix the ground beef with salt and pepper. Be careful not to overmix.
Divide the beef mixture into 4 equal portions and form them into patties, slightly larger than your burger buns. Make a small indentation in the center of each patty to prevent them from puffing up too much.
In a small bowl, combine the softened butter, minced garlic, and chopped parsley. Mix well until everything is incorporated.
Heat a grill or a skillet over medium-high heat. Cook the patties for about 4-5 minutes per side for medium-rare, or longer for your desired doneness.
During the last minute of cooking, top each patty with a slice of cheese and let it melt.
While the burgers are cooking, lightly toast the burger buns if desired.
Spread a generous amount of the garlic-parsley butter mixture onto the top bun of each burger.
Assemble the burgers by placing a cheese-topped patty on the bottom bun, then adding lettuce, tomato, and onion if using. Place the buttered top bun on top.
Serve immediately and enjoy your Wisconsin Butter Burgers!
Notes
These burgers are incredibly rich and flavorful. You can customize the toppings to your preference.