Put chopped onion, ground meat, egg, bread crumbs, salt and pepper in a large bowl. Mix very well. Divide meat mixture into 4 pieces. Form flat oval shapes.

In a large frying pan, heat oil at medium heat, put the meat patties in the pan, and cook. When one side is browned, turn over, cover, and cook for a few minutes. Take them out onto a plate and set aside.

In a clean large pan, heat butter at medium heat, and cook sliced onion and mushrooms until soft. Sprinkle with flour and cook for a couple of minutes. Add broth, ketchup, Worcestershire sauce, soy sauce, and sugar. Stir and cook for a minute. Add cooked patties in the sauce, and cook for 10 minutes covered.

Top with chopped parsley if you like.