Peel and wash the carrots, cut them in half lengthwise and cut into pieces. Clean and wash the cauliflower and cut into small florets. Clean, wash and cut the leek into pieces. Clean, wash, halve or quarter mushrooms. Grate cheese. Cook carrots and cauliflower in boiling salted water for about 15 minutes.
Add leek for the last 5 minutes. Heat oil in a pan and fry mushrooms for about 5 minutes. Put the vegetables on a sieve, collect the vegetable water and measure 3/8 litres. Melt the fat in a pot. Sweat flour in it, add vegetable water and cream while stirring. Stir 2/3 cheese into the sauce, season with salt and pepper. Put the vegetables and mushrooms in an ovenproof casserole dish and spread the sauce over them. Peel, wash and coarsely grate the potatoes. Stir in egg and remaining cheese. Season to taste with salt, pepper and nutmeg. Spread the potato mixture over the vegetables.
Stir 2/3 cheese into the sauce, season with salt and pepper. Put the vegetables and mushrooms in an ovenproof casserole dish and spread the sauce over them. Peel, wash and coarsely grate the potatoes. Stir in egg and remaining cheese. Season to taste with salt, pepper and nutmeg. Spread the potato mixture over the vegetables. Bake in the preheated oven (electric cooker: 200 °C/ gas: level 3) for about 30 minutes. Serve the vegetable casserole garnished with herbs
Preparation time approx. 1 1/4 hours