In a small bowl, mix all the spice blend ingredients together. Set aside.
In a large bowl, combine olive oil, 3 tbsp of the spice blend, sumac, salt, and lemon juice. Mix well.
Add the chicken quarters and coat them evenly with the marinade.
Cover and let it marinate for at least 1 hour (overnight for best results).
Preheat your oven to 200°C (400°F).
Place the marinated chicken in a baking dish and pour the chicken broth into the dish.
Cover with foil and roast for 35-40 minutes.
Remove the foil, increase the oven temperature to 220°C (430°F), and roast for another 15 minutes or until the chicken skin is crispy and golden brown.
Heat olive oil in a large pan over medium heat.
Add the chopped onions, spice blend, salt, sumac and mix well.
Cook until soft and caramelized (about 20-25 minutes), stirring occasionally.
Remove from heat and set aside.
Preheat the oven to 190°C (350°F).
Place the flatbreads on a baking tray and spread a generous layer of the spiced onions over them.
Place the roasted chicken on top and drizzle any remaining juices from the baking dish.
Sprinkle with extra sumac, toasted pine nuts, and chopped coriander.
Place the assembled dish in the oven for 5 minutes to warm through.
Serve hot! Traditionally, Musakhan is eaten with hands, tearing off pieces of bread with chicken and onions. Enjoy the bold flavors and rich textures with every bite!