Bone and skin the chicken breast, season with salt and pepper and fry in butter until cooked. Remove from the pan and keep warm.
Chop the white part of the leek only (reserve the green part) and add, along with the shallot, to the pan in which you fried the chicken. Add the wine and reduce until the leek and shallots are moist. Add the veal stock. Reduce a little until syrupy and add th