Place 2 lasagne plates in boiling salted water and cook for about 7 minutes. Quench and let them drain side by side. Process remaining lasagne plates in the same way. In the meantime, wash the asparagus and cut off the woody ends. Cut asparagus into large pieces, put them into boiling pasta water with 1 teaspoon sugar, bring to the boil and cook for about 4 minutes. Pour into a sieve, quench and drain well
Peel and finely chop the onion. Melt butter in a pot and fry onion until transparent. Dust with flour, sweat and gradually add stock, wine and cream, stirring continuously. Bring to the boil and simmer for about 2 minutes at low heat while stirring. Season to taste with salt and pepper. Wash the chervil, shake dry and chop finely. Stir half of the chervil into the sauce
Pick salmon. Grease a grease pan of the oven. Place the lasagne plates one by one on top, cover half of them with some asparagus and half of the salmon, drizzle some sauce over them and fold them over. Use the rest of the lasagne sheets in the same way. Spread the rest of the sauce over the lasagne sheets. Sprinkle with cheese and bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 12 minutes. Remove from the oven and arrange on plates sprinkled with remaining chervil