This is the first recipe Yashim cooks in The Janissary Tree, and his friend Palewski guesses what it is by sniffing. You can also make it with duck, or pheasant, after which it is named in Persian Fesenjan.
Toast the walnuts in a dry frying pan over a fairly hot hob. Stir them until they catch, then cool them down and grind them fairly fine in a blender or pound in a mortar.
Melt half the butter and oil together, and brown the chicken with a pinch of salt. Remove to a plate.
Put the rest of the oil and butter in the pan, lower the heat, and fry the onions to