1. Preparing the patties:
In a bowl, mix the ground meat with salt, pepper, mustard, and Worcestershire sauce. Combine well, but do not overmix to keep the patties juicy.
Shape into 4 patties about 1.5 cm thick. Place them in the fridge while you prepare the other ingredients.

2. Creamy Belgrader sauce:
In a small saucepan, melt the butter over medium heat, then add the finely chopped garlic. Sauté for about 1 minute until fragrant.
Add the cooking cream and Belgrader cheese. Stir until the cheese melts and the sauce becomes smooth and creamy.
Add a pinch of pepper and nutmeg (if desired) for extra depth of flavor.
Remove from heat and let it cool slightly — the sauce will thicken as it rests.

3. Cooking the patties:
Heat a pan or grill over medium heat. Add a little olive oil and cook the patties for 4–5 minutes on each side, until nicely browned on the outside and juicy inside.
Towards the end, you can place an extra thin slice of Belgrader cheese on each patty to let it melt slightly.

4. Preparing the onion:
Heat olive oil in a pan and add the red onion rings. Cook over medium heat for 5–7 minutes until soft and lightly caramelized.

5. Preparing the buns:
Slice the buns in half and toast them on a dry pan or grill until golden and slightly crispy.

6. Assembling the burger:
Spread a layer of ajvar (optional) on the bottom half of the bun.
Add lettuce or arugula.
Place the patty with melted Belgrader cheese on top.
Spoon the creamy Belgrader sauce over the patty.
Add a slice of tomato and caramelized red onion.
Cover with the top half of the bun.