Clean the carrots and kohlrabi, cut evenly into long strips. Shell the peas. Cook these three vegetables in salted water till just tender.
Peel the white asparagus, cut the spears into pieces about the length of a finger, steam in a light vegetable broth.
Cut the cauliflower and cook in water or milk, adding some butter and salt.
Cut the morel mushrooms into halves and sauté in butter.
Boil the crayfish, and split into pieces, carefully removing the meat from the tails. Rub the head of the crayfish with salt.
Whisk about 2 ounces of the butter until light. Separate the eggs. Beat the egg whites until foamy. Fold the egg yolks, egg whites, mace and breadcrumbs into the whisked butter and fill the crayfish head with this mixture. Form the remaining mixture into dumplings and cook these in boiling salt water for 5 minutes.
Use about 3.5 ounces of the butter and the flour to start a roux in a pan; add a bit of the asparagus and cauliflower water to make a thick sauce.
Brown the remainder of the butter, and set aside. Place the mixed vegetables, except the morels, into a serving bowl. Add some of the roux sauce, then the crayfish tails and dumplings, sprinkle with browned butter, and add the morels, crayfish legs and heads. Pour the sauce over it. Then add the dumplings and crayfish tails. Drizzle everything with brown butter, and arrange the morels, and crayfish heads and claws on top.