Start by heating a tablespoon of butter in a skillet over medium heat. Add the sliced onions and a pinch of salt, cooking them slowly until they’re caramelized and golden brown, about 10 minutes. Stir occasionally to avoid burning.

While the onions are cooking, divide the ground beef into equal portions and form them into patties. Season both sides with salt and pepper.

In another skillet, add 1 tablespoon of butter and heat it over medium-high heat. Place the burger patties in the skillet and sear for about 3-4 minutes on each side, or until cooked to your preference. During the last minute of cooking, place a slice of cheese on each patty to melt.

Spread butter on one side of each slice of bread. Layer one slice butter-side down in the skillet. Top with a cheesy patty, some caramelized onions, and another slice of bread, butter-side up.

Grill each sandwich for about 3-4 minutes on medium heat, pressing down slightly, until golden brown. Flip carefully and repeat on the other side until both sides are golden and the cheese is melted.

Remove the sandwiches from the skillet, slice them in half, and serve hot!