Msakhan (Palestinian Flatbreads With Onion, Sumac, and Spiced Roast Chicken)

For the chicken: Adjust oven rack to middle position and preheat oven to 450°F (230°C). Line a rimmed baking sheet with parchment. In a small bowl, stir together the olive oil, sumac, allspice, black pepper, and cumin. Arrange chicken, skin side up, on prepared baking sheet and season all over with salt. Rub all over with spiced oil, pushing some under the skin. Roast chicken until an instant-read thermometer inserted into the thickest part registers 150°F (66°C) for the breast, about 25 minutes, or 175°F (80°C) for the legs, about 30 minutes. Let chicken rest 15 minutes, reserving any accumulated juices for the onions. Serious Eats / Vicky Wasik Meanwhile, for the onions: In a medium Dutch oven or large skillet or sauté pan set over medium-low heat, stir together the olive oil, onions, and salt, and cook, stirring occasionally, until the onions have softened completely and are turning golden around some edges, about 30 minutes; adjust heat as needed to either speed up or slow down the rate of cooking so that it's gentle but active. Serious Eats / Vicky Wasik Stir in the sumac, cumin, cinnamon, black pepper, and chicken broth, along with any reserved chicken juices, and cook, stirring often, until onions have cooked down to a jammy and glazed consistency, about 10 minutes longer. Remove from the heat and set aside. Serious Eats / Vicky Wasik To serve: Turn on broiler and position top rack about 4 to 6 inches from broiler element. Line a rimmed baking sheet with parchment. Working with one flatbread at a time, moisten the edges of each flatbread by dipping it into the oily glaze on the surface of the onion mixture and rotating it around. Set the flatbread on the prepared baking sheet. Serious Eats / Vicky Wasik Spoon about a quarter of the onion mixture onto the flatbread and spread it around in an even layer, leaving a thin border around the edge (similar to pizza). Sprinkle all over with sumac and toasted pine nuts. Repeat with remaining flatbreads, onions, sumac, and pine nuts, stacking them one on top of the other (this keeps them moist, especially as you start to broil them). Serious Eats / Vicky Wasik If chicken has cooled too much, insert it under the broiler just long enough to rewarm and re-crisp the skin. Working with one or two flat breads at a time, arrange in a single layer on a baking sheet and broil until the flatbread's edges have browned in spots, 1 to 4 minutes (keep a close eye on them as broiler strength can vary quite a bit). Transfer each flatbread to a plate, top with a whole piece of chicken, and serve. Serious Eats / Vicky Wasik