Clean and singe the chicken, as if for roasting, and cut into four pieces – two with the wings and two with the legs. Make a small incision between the drumstick and the thigh of the chicken to speed the cooking process. Cut off the last joint of the wings.
Wash the herbs in several waters and drain carefully. Detach each leaf of chervil and watercress, and throw away the stalks. Do the same with the tarragon, but keep the stalks. Pull the green parts of the sorrel leaves away from the central stalk and roll them up like cigars. Cut each ‘cigar’ in fine slices to obtain thin ribbons called a chiffonade. Pick over the spinach and wash in several waters. Drain carefully, remove the stalks and make a chiffonade in the same way as for the sorrel. Peel the shallots and chop them.
Butter the bottom of an enamelled cast-iron casserole generously, with 30g (1oz) of butter. Strew it with chopped shallots. Salt and pepper each piece of chicken and place them on the bottom of the casserole. Add the tarragon, cover, and cook very gently over a very low heat for 25 minutes. The chicken should remain white and the butter should not have coloured. For this operation, known as cooking à l’étuvée, it is vital that the heat be very low and the lid of the casserole tightly fitting. When the chicken is done a knife point inserted in the thigh will produce a bead of colourless liquid. If the liquid is still rosy, continue the cooking for a few minutes more.
While the chicken is cooking, put 20g (¾oz) butter to heat in a large saucepan over a fierce heat. Throw in the spinach (2) and stir with a wooden spatula until there is not a drop of water left. Add the rest of the herbs (chervil, sorrel, tarragon, watercress) and let them wilt over the heat, stirring with the spatula for 3–4 minutes. Put on one side, uncovered.
When the chicken is cooked remove it from the casserole and keep hot. Return the casserole to the stove, take out the tarragon stalk, turn up the heat, add 5tablespoons of the cream and allow to boil for 3–4 minutes. Mix the remaining cream with the egg yolk in a bowl. Add the herbs and vegetables (4) to the casserole, bring almost to boiling point and remove from the heat. Pour in the egg/cream mixture and mix well. Allow the sauce to thicken a little over a very low heat. Season with salt and pepper. Arrange the pieces of chicken on hot plates and cover with the sauce. The garden has come to your table!
a mellow white wine such as Mâcon, Burgundy, Pouilly fumé