Mix the eggs, 1 pinch of salt and milk. Stir in 150 g flour. Let the dough swell for at least 20 minutes.
Wash and peel the asparagus and generously cut off the woody ends. Cook the asparagus in plenty of boiling salted water, covered with 1 teaspoon sugar, for about 10 minutes. Drain well, catch the asparagus cooking water.
Stir mineral water into the pancake batter. Heat the clarified butter in portions in a small coated pan (approx. 20 cm Ø). Bake 8 thin pancakes from the batter one after the other.
Finely grate the cheese. Heat butter.
Lightly sauté 2 tbsp. flour in it. Add cream and 400 ml cooking water and bring to the boil while stirring. Stir in stock and simmer the sauce for about 5 minutes. Melt half the cheese in the sauce. Season with pepper, nutmeg and a little salt.
Cover each pancake with 1 slice of ham. Spread asparagus on top. Roll up the pancakes. Place in portions in four ovenproof moulds or a large mould. Pour the sauce over the pancakes and sprinkle with the remaining cheese.
Bake in the preheated oven (electric oven: 200 °C/circulating air: 175 °C/gas: level 3) for 18-20 minutes. Finally garnish with chervil.