Wash and peel the asparagus, cut off the woody ends. Cook the stalks in 1⁄2 l boiling salted water covered with 1 teaspoon sugar for about 10 minutes. Wash potatoes and cook covered for about 20 minutes.
Romanesco clean, wash, cut into florets. Cook in boiling salted water for about 8 minutes.
Lift the asparagus out of the water and let it drain. Measure 350 ml of cooking water. Drain Romanesco. Drain potatoes, quench, peel and, depending on size, possibly halve them.
Grate cheese. Peel and finely chop the onion. Heat butter in a pot. Sauté onion in it. Dust with flour and sweat it. Stir in cream and asparagus water. Bring to the boil and simmer for about 5 minutes.
Melt just under half the cheese in the sauce. Season to taste with salt and pepper.
Dab meat dry. Cut pork fillet into 8, beef fillet into 4 medallions. Heat oil in a pan. Fry the medallions in portions on each side for 1 minute over high heat. Season with salt and pepper.
Place the vegetables and potatoes in one large or two small ovenproof dishes. Arrange medallions on top. Pour sauce over them. Sprinkle with remaining cheese. Put them in a preheated oven.
(electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer) Bake for 15-18 minutes. Wash parsley, shake dry and chop finely. Sprinkle the gratin with parsley.
Drink tip: dry white wine, e.g. a full-bodied Pinot Gris.