Cook the crayfish—previously prepared*—in court-bouillon or salted water for 4 minutes, then cool under cold running water. Separate the heads from the tails of 28 crayfish, reserving 4 whole ones. Save the heads, shell the tails, and keep them warm.
Heat the olive oil in a saucepan, add the crayfish heads, and brown well. Stir in chopped carrot, onion, and celery. Deglaze with cognac, reduce, then add white wine and bouquet garni. Simmer for 5 minutes, pour in 2 liters of water, and cook for 20 minutes. Strain through a fine sieve, pressing to extract all juices. Reduce the stock to about 2 glasses (20 cl) and set aside.
In a sauté pan, combine champagne and sugar, simmering gently until it begins to caramelize. Add cream and reduced crayfish stock, then reduce further.
Arrange the shelled tails in porcelain egg cups* (or prepared boiled eggs for a creative twist). Place on plates, garnish with whole crayfish, and warm in a hot oven for 2 minutes. Season the sauce with two turns of the pepper mill and salt. Pour over the tails and finish with chervil sprigs.
*Have your fishmonger remove the central gut tract from live crayfish.
*Alternatively, halve boiled eggs, remove yolks and membrane, then fill—more original but labor-intensive.
Joëlle's Tip: Trussing crayfish (folding legs back and securing claws to tail) is tricky. Do it with live ones per the chef's advice—they curl naturally. Easier said than done!
