Divide the ground beef into 4 equal portions and shape into patties approximately 1/2 inch thick.

Season both sides of the patties liberally with salt and pepper.

Heat a large skillet over medium high heat. Add the patties to the pan and cook for 4-5 minutes. Flip the burgers and cook for an additional 3-4 minutes or until the desired degree of doneness.

Transfer the burgers to a platter and keep warm. Wipe out the skillet with a paper towel and return to the heat.

Melt the butter in the pan and add four slices of bread. Top each slice of bread with a slice of cheese, then top with the burger patties. Layer a slice of cheese over the burger and spread 2 tablespoons dressing on each. Top with 1/4 cup caramelized onions and the remaining slices of bread on each.

Press down on each sandwich gently with a spatula and cook for 1-2 minutes. Carefully flip each sandwich over and continue cooking for an additional 1-2 minutes (adding more butter, if necessary).

Slice in half and serve immediately with extra dressing on the side, if desired.