Remove the claws from the crabs and quarter the bodies. Heat a 6-quart stockpot. Add the oil and saute the crab pieces until they are red. Remove the pieces as they are cooked. Add the carrot, celery, tomatoes, garlic, shallots, and tarragon and continue to saute for 10 minutes. Pour in the cognac and ignite. When the flame has subsided, deglaze with white wine, and add the tomato paste, crab, and enough fish stock to cover. Season with salt, pepper, cayenne, thyme, and bay leaf and boil gently for 15 minutes.
In a small saucepan, reduce the cream by half. Remove the crab bodies from the pot and set aside. Add the reduced cream to the soup. Puree the soup, in batches, in a food processor. Strain the pureed soup and keep warm.
Remove the meat from the claws and cut into bite-size pieces and add to the soup. Season with lemon juice, salt, and pepper. Serve in heated soup bowls and garnish with minced chives or parsley.
Recipe courtesy of Wolfgang Puck, Modern French Cooking for the American Kitchen: Houghton Mifflin, 1981