Beef cut into fine slices, place individually on a board, spread thinly and cut into pieces about 5 cm. Clean leeks, cut into rings, rinse and drain.
Cream butter in a lidded pan. Pour in the meat, roast for 1 minute, turning, and transfer to a plate. Add one-eighth of a liter of water, gravy, and leeks to the roasting pan, then top with the meat. Season with salt and pepper. Cover and cook for 5 minutes until tender. Later turn to the other side, season and serve.
Serve with: Mashed potatoes or boiled potatoes.