In a large skillet, heat 2 tablespoons of olive oil and 1 tablespoon of butter over medium heat until melted and bubbling. Add 2 large thinly sliced onions to the pan, stirring to coat them evenly. Allow the onions to cook for about 15–20 minutes, stirring occasionally, until they turn golden brown and sweetly caramelized.

While the onions are caramelizing, take 1 pound of ground beef and divide it into four equal portions. Gently form each portion into a burger patty, ensuring not to overwork the meat, which helps maintain juiciness.

Generously season both sides of each patty with salt and pepper to enhance the flavor.

In a separate skillet or on a hot grill, place the seasoned patties over medium-high heat. Cook for about 4–5 minutes on each side, or until they reach your desired doneness.

If you’re including cheese, place a slice on each patty during the last minute of cooking to melt.

While your patties finish cooking, lightly toast the burger buns in a toaster or on the grill for about 2 minutes until golden.

To assemble, start with the bottom half of the toasted bun. Layer it with fresh lettuce, followed by the juicy burger patty with melted cheese, and generously pile on the sweet caramelized onions.

Finish your burger by adding any additional toppings or sauces you desire, and place the top half of the bun on your stack and serve immediately.