Begin by slicing the white onion into thin rings. The thinner the slices, the better they will caramelize and meld into the burger. Set them aside as we prepare the beef.
In a large bowl, combine the ground beef, Kosher salt, and cracked black pepper. Mix gently with your hands until the seasonings are evenly distributed. Be careful not to overwork the meat, as this can lead to tough burgers.
Divide the seasoned beef into four equal portions and shape them into patties. Make sure to create a slight indentation in the center of each patty to help them cook evenly.
In a large skillet or griddle, melt 2 tablespoons of butter over medium heat. Add the sliced onions and cook, stirring frequently, until they become soft and golden brown—about 10 to 15 minutes. Once done, remove them from the skillet and set aside.
In the same skillet, add the remaining 2 tablespoons of butter. Increase the heat to medium-high and place the burger patties in the skillet. Cook for about 3-4 minutes on one side, then flip the patties.
After flipping, immediately place a generous amount of the caramelized onions on top of each patty. This will allow the flavors to meld beautifully.
Place a slice of American cheese on each patty and cover the skillet with a lid. This will help the cheese melt perfectly—about 1-2 minutes should do the trick.
Once the cheese is melted and the burgers are cooked to your desired doneness, remove them from the skillet. Place each burger on a bun, and feel free to add any additional toppings you love, such as pickles or mustard.
