Place all the seasoning ingredients in a small bowl and mix well.
Preheat the oven to 420°F / 220°C.
In an oven-safe pan, add the onions, sweet potatoes, olive oil, salt, black pepper, and sumac. Mix well and spread everything into an even layer.
Arrange the chicken leg quarters on top.
Spoon the chicken seasoning over each piece of chicken and spread it evenly.
Cover with wet parchment paper, then foil, and bake at 420°F for 1 hour.
Remove the parchment and foil and bake uncovered for another 15 minutes.
Set the oven to broil at 450°F and broil for 6-7 minutes, until the chicken is beautifully golden and caramelized.
Garnish with chopped cilantro or parsley and flaky Maldon salt.
