1. Heat butter or olive oil in a saucepan over medium-low heat. Add sliced onions and slow cook for 15 minutes, stirring occasionally, until golden brown. Remove from heat and set aside.

2. Divide the ground beef into 4 equal portions, gently form into balls without packing tightly.

3. Heat up a heavy-duty stove or grill over a hot flame. Place beef balls on the frying pan and crush firmly with a spatula to form thin patties.

4. Cook for 2-3 minutes without moving then flip. Immediately add slices of cheese on top and cook for 1-2 minutes until cheese is melted and burger is cooked. Season with salt and pepper.

5. Buns spread slightly on the pan.

6. Assemble burgers by placing patties on buns, top with caramelized onions, lettuce, tomatoes, pickles and dill.