Le Ris de Veau à la Sauce aux Truffes

• 700 g (1½ lb) calf’s sweetbreads
• 1 large onion, finely chopped

Soak the sweetbreads whole for several hours, changing the water as often as possible. Blanch them in boiling water for 5 minutes, then lift out and take off the membrane encasing them as well as any fat or other waste.

Sweat the onion very slowly in a tablespoonful of the fat for about 30 minutes. Use a wire gauze mat if you cannot get the heat low enough (because the onion must not co