Season the pieces of chicken and stiffen them in butter without colour. Add 100 g (3½ oz) sliced white of leek and 50 g (2 oz) sliced onion both previously cooked in butter. Cover with a lid and finish cooking in the oven.
About 5 minutes before the chicken is cooked, add 100 g (3½ oz) sliced mushrooms sautéed in butter and complete the cooking.
When cooked, arrange the chicken in a deep dish. Add 1 dl (3½ fl oz or ½ U.S. cup) each of cream and Velouté to the vegetables in the pan, reduce by half then pour this sauce and the vegetables over the chicken.