Bring the court bouillon to the boil, plunge in the crab and
Peel the asparagus tips if they need it, then tie them into bundles of fives. Trim the tips so that they are about 10 cm/4 inches long. Pick the chervil leaves from their stalks. Cut the butter into 1 cm/½ inch cubes and leave in the refrigerator. Combine the fish stock and dry sherry together, set over a high heat and reduce by three-quarters.
Lightly butter 8 oval or round
Meanwhile, add the cream to the reduced stock, bring back to the boil and then remove from the heat. Gradually add the butter a piece at a time, whisking continuously until it has all melted. Plunge the asparagus tips into boiling water and cook until they still have a little bite, about 2 minutes. Remove and drain.