Clean and wash the leek and peppers. Cut the leek into thick rings and the paprika into cubes. Clean the mushrooms and, depending on their size, possibly halve them. Pre-cook leek and paprika in 1/4 litre boiling water with little salt for about 5 minutes. In the meantime heat oil in a pan and fry the mushrooms until golden brown. Pour the leek and peppers onto a sieve and collect the vegetable water.
Measure out a good 1/8 litre and pour into the pan with the cream to go with the mushrooms. Stir in Fix for gratin and bring to the boil briefly. Fold in leek and paprika and distribute in two greased gratin dishes. Sprinkle with cheese and bake in the preheated oven (electric: 200 °C/ gas: level 3) for about 15 minutes. Serve garnished with fresh oregano and rosemary