Difficulty: Medium
Peel, seed, and cut the cucumber into fine brunoise dice. Salt and soak for 1 hour, then rinse thoroughly. Peel and seed the tomatoes, dicing them to match the cucumber size. Trim and dice the mushrooms similarly.
Bring 1 liter of water to a boil with the coarse salt. Blanch all diced vegetables until al dente, then refresh under cold running water.
Melt 2 knobs of butter in a sauté pan over high heat. Add the vegetables, reduce heat, cover, and cook gently for 15 minutes. Pour in the vermouth and simmer for 10 minutes. Stir in the whipping cream, season to taste, and finish with chopped chervil.
Gently fold the crab meat into the vegetable mixture.
Butter a gratin dish. Layer lasagna sheets and crab filling alternately until ingredients are used up. Pour over the veal jus, sprinkle with thyme, and bake for 25 minutes in a preheated medium oven (thermostat 7, about 425°F).
Just before serving, dot with the remaining 2 knobs of butter.
Serve hot, straight from the dish.
