Soak porcini mushrooms in 1/4 litre of warm water for 30 minutes. Clean, wash and cut cabbage into slices. Blanch in boiling salt water for five minutes. Quench cold, drain.
Clean, wash and slice the tomatoes. Clean, wash and halve the mushrooms according to size. Drain porcini mushrooms (collect liquid), chop coarsely. Peel and chop onion and garlic and fry in hot fat.
Fry the mushrooms. Sprinkle with flour, sweat and deglaze with mushroom water and milk. Let simmer for about five minutes. Whisk the egg yolks and crème fraîche, stir into the sauce, do not boil any more.
Flavour with salt, pepper and nutmeg. Place the prepared vegetables in an ovenproof dish. Cover with sauce and bake in a preheated oven (electric: 200°C / gas: level 3) for 15 minutes.
Wash the chives, put aside some tips with flowers for garnishing. Cut the rest into small rolls. Serve the casserole garnished with chive rolls and flowers.