Boil lasagna noodles in salted water until al dente. Rinse asparagus and trim off the bottom third. Chop stalks into segments. Remove lasagna sheets with a slotted spoon and drain. Cook asparagus in pasta water for about 5 minutes, then remove and drain. Wash parsley, pat dry and chop. Wash trout fillets, pat dry, cut into 8 equal strips and season with salt and pepper. Fill lasagna with asparagus, fish and some chervil. Place in a baking dish greased with 1 tablespoon butter. Boil broth mixed with cornstarch, stirring constantly. Reduce the heat and add wine, egg yolks and remaining butter.
Whip cream until stiff peaks form. Fold into the sauce. Season with salt, pepper, nutmeg and a pinch of sugar. Add remaining chervil.
Pour sauce over stuffed lasagne in baking dish. Bake in an oven preheated to 200°C (approximately 400°F) on the middle rack for about 20 minutes. Remove and serve.