Crayfish with Asparagus

In a large pot, heat water, vinegar, wine, bay leaves, chopped soup vegetables and peppercorns. Add crayfish, bring to a boil and leave for about 15 minutes. Add asparagus tips and simmer for 15 more minutes. Add cream fraiche and allow to reduce slightly. Season with saffron, salt and pepper, then stir in butter. Remove heads from crayfish, cut shell on underside and detach meat. Cut meat into slices and serve with asparagus tips on warmed plates. Divide caviar on plates, pour sauce over dish and serve garnished with chervil leaves.