Method
Season the chicken with salt and pepper and set it aside while the onions cook. There is no marinating step here; the flavour comes from what it roasts on top of.
Warm the olive oil in a wide pot and add the onions with a pinch of salt. Cook them low and slow, stirring occasionally, until they collapse and turn deep gold — this takes a genuine 25 to 30 minutes and is not a step to rush.
Off the heat, stir the sumac, allspice and cinnamon through the onions. Taste — sumac varies a lot in sourness between brands, so adjust here rather than guessing at the start.
Spread half the onions over the base of a roasting tray, lay the bread on top, then spread the remaining onions over the bread and arrange the chicken pieces on top, skin side up.
Roast at 200°C (400°F) for 35 to 40 minutes, until the chicken is cooked through and the skin has coloured. The bread underneath will have soaked up the oil and onion juices and turned soft and rich — that layer is the point of the dish.
Scatter with pine nuts and an extra pinch of sumac before serving. Eaten by hand, with the bread torn and eaten along with the chicken and onions rather than served plain on the side.
Notes
The onions should be cooked down fully before the tray goes in the oven — they will not reduce further while roasting, so any raw sharpness at this stage stays in the finished dish.
Some households add a spoon of tahini sauce over the top; others keep it plain. Both are common.