The day before

1. Clean the sweetbreads.
2. Place the sweetbreads in a bowl of ice water to rid them of any impurities. Soak for three hours, changing the water two or three times. Remove the thin membrane surrounding the sweetbreads, and blanch in boiling water for 2 minutes. Drain. Refrigerate until the next day.

The day of serving

1. Quarter the lemon, place the pieces into a saucepan, barely cover with water and add the sugar. Bring to a boil over high heat, reduce the heat and continue cooking for 30 minutes over low heat to candy the lemon.
2. Peel the carrot, onion and celery. Chop finely and put into an ovenproof casserole with a knob of butter; place over low heat and let sweat gently until lightly colored.
3. In a sauté pan, heat 60 g butter and brown the sweetbreads on all sides. Place them on top of the vegetable garnish in the casserole. Add veal stock to half cover the vegetables and bring to a boil.
4. Preheat the oven to 200° C (400° F). Cover the casserole and place into the oven for 15 to 20 minutes.
5. Clean the chanterelles and wash them in several changes of water. Cook covered for 3 minutes in the remaining butter with a glass of chicken stock. Drain, reserving the liquid.
6. Peel the asparagus and trim the stalks to the same height. Cook for 12 minutes in simmering salted water. Drain and plunge into cold water. Drain again.
7. Remove the sweetbreads from the casserole, slice them thinly and divide them among deep warm plates; season lightly with salt and pepper. Pour the juice from the chanterelles through a fine mesh strainer into the casserole.
8. Blend this juice with the rest of the cooking liquid, and reheat the chanterelles and asparagus in it.
9. Add the preserved lemon, cut into thin strips.
10. Divide the mixture over the sweetbreads, ladle the hot broth over top and serve immediately.