Finely chop fresh chervil, mix it with 50 g of butter, put in the fridge (in a roll), leave to harden.
Wash and cook the langoustines in court-bouillon, shell them and reserve the tails.
Drain the sweetbreads, blanch them and cool them. Brown them in butter in an ovenproof dish, add the carrot cut into slices and the minced onion, then the bouquet garni. Wet with the glass of white wine, dilute with a little water, braise in the oven for about 10 minutes.
As soon as they are cooked, drain the sweetbreads, degrease them, remove their nerves and trim them as much as possible, then slice them into medallions. Strain the cooking juices through cheesecloth, set aside. In a frying pan, put 1 knob of butter, quickly sear the medallions on each side, pat them dry. Then throw the langoustine tails into the cooking butter, sear them on each side*, pat them dry.
Arrange the medallions on plates, then the tails around.
In the cooking pan, put 2 tablespoons of the cooking juices from the sweetbreads, leave to bubble for a few seconds and winnow with the chervil butter, salt and ground pepper.
Put the plates in the oven quickly and cover with the sauce.
* You can keep the heads.
My advice:it is very important that the sweetbreads are completely denervated, the slightest nerve or small skin remaining would affect the quality of the dish.
