Clean and wash the leek and cut into wide rings. Clean the mushrooms, wash if necessary and cut in half.
Dab meat dry and cut into thick medallions. Heat 1 tablespoon of oil in a frying pan. Brown the medallions on each side. Season with salt and pepper and remove.
Heat 2 tablespoons of oil in the frying fat. Fry the mushrooms and leek for about 5 minutes and season with salt, pepper and marjoram. Add cream and 300 ml water. Bring to the boil, stir in broth and simmer for 2-3 minutes.
Stir starch and 3 tablespoons of water until smooth. Stir into the sauce and simmer for 1 minute. Season to taste with salt and pepper.
Pour the mushroom and leek vegetables with sauce into an ovenproof dish. Place medallions inside. Grate the Gouda and sprinkle over the medallions. Bake in a preheated oven (electric: 200 °C/circulating: 175 °C/gas: level 3) for 15-20 minutes.
Baguette or Spätzle taste good with it. Drink tip: a gentle red wine, e.g. a dry Pinot noir.