Season ground beef with salt and pepper. Knead mixture, form two meat patties and flatten. Cook almost through on hot grill or frying pan, while flattening patties.
Slice hamburger bun in half and toast lightly on cut surfaces. Cover bottom half of bun with endive leaves. Season to taste with ketchup and mustard. Cover first patty while it is still hot with one slice of Emmental AOP, then add second patty and cover with another cheese slice.
Garnish with tomato and gherkin slices and onion rings. Add mayonnaise, mustard and ketchup and cover with top half of bun.