Cook the crayfish in court-bouillon or salted water for 4 minutes and cool. Separate the heads from the tails of 28 crayfish and set aside 4 whole. Reserve the heads, peel the tails, keep warm.
Put the olive oil in a saucepan on the fire, throw in the crayfish chests, let brown well, add the carrot, the onion and the celery. Deglaze with the cognac, let reduce, add the white wine then the bouquet garni. Boil for 5 minutes and add 2 liters of water. Let cook for 20 minutes. Then pass through a fine sieve, pressing well on the elements to collect all the juices. Put this juice back to reduce until you obtain about 2 glasses (20 cl) of liquid. Set aside.
Put the champagne and the sugar in a sauté pan, cook gently until the caramelization begins to take place. At this point add the cream and the crayfish stock. Let reduce again.
Distribute the crayfish tails in porcelain egg cups, place them on plates, decorate with the whole crayfish. Place in the hot oven for 2 minutes.
The cooking having reduced by half, give two turns of the pepper mill and salt. Take out the egg cups and distribute the sauce in each, adding a few sprigs of chervil.
Note:In the photo you can see the crayfish standing directly in eggshells, of course it's more "pro", but it requires a lot more work!
