For the dough, mix eggs, salt, pepper and nutmeg. Alternately stir in flour and milk. Leave to swell for about 30 minutes.
Wash and peel the asparagus, cut the ends off generously. Stir mineral water into the dough. Heat lard in portions in a pan (approx. 20 cm Ø). Fry 6 thin pancakes one after the other until golden brown.
Wash the chervil, remove coarse stalks. Spread a thin layer of crème fraiche on the pancakes. Spread chervil on top. Roll up 3 pancakes with salmon, the others with ham, tightly. Cut diagonally into 1.5-2 cm thick slices.
Place the rolls on a baking tray lined with baking paper. Grate cheese over it. Bake in the preheated oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer) for approx. 12 minutes.
Bring plenty of salted water and sugar to the boil. Cook the asparagus for about 12 minutes. Peel and chop the onion. Wash the tomatoes and halve them according to size. Heat the oil in a pan. Steam the onion for about 2 minutes.
Add the tomatoes and steam briefly. Sprinkle with brown sugar, melt carefully. Season with salt and pepper and deglaze with vinegar. Simmer at low heat for 4-5 minutes.
Drain the asparagus. Serve with melted tomatoes and crespelle.