Step 1: Caramelize the Onions

1. Peel and thinly slice the onions into rings.
2. In a large pan, melt 2 tablespoons of butter over medium-low heat.
3. Add the sliced onions and sprinkle with 1 teaspoon of sea salt.
4. Cook slowly, stirring occasionally, for about 10 minutes.
5. Add 2 tablespoons of water to help soften the onions and deglaze the pan.
6. Continue cooking, stirring occasionally, for another 20-30 minutes until the onions are soft and golden brown.

Step 2: Prepare the Beef Patties

1. Divide the ground beef into four equal portions and shape them into thick, round patties.
2. Generously season both sides with salt and black pepper.
3. In a large pan, melt 1-2 tablespoons of butter over medium heat.
4. Place the patties in the pan and fry for about 5 minutes per side, until well browned on the outside and cooked through.
5. Remove the patties from the pan and set them aside. Keep them warm while making the sauce.

Step 3: Make the Sauce (Gravy)

1. In the same pan where the patties were cooked, melt 2 tablespoons of butter over medium heat.
2. Whisk in 3 tablespoons of flour and cook, stirring constantly, for 1-2 minutes, until the flour turns light golden brown.
3. Gradually add the veal or beef stock, whisking continuously to prevent lumps.
4. Continue whisking until the sauce thickens.
5. Season with salt and black pepper to taste.

Step 4: Assemble and Serve

1. Place the beef patties on a serving plate.
2. Top each patty with a generous portion of caramelized onions.
3. Drizzle the pan sauce (gravy) over the patties.
4. Serve with boiled or oven-roasted potatoes and pickled cucumber on the side.