In a large bowl, whisk together yogurt, mayonnaise, tomato paste, cumin, coriander, paprika, salt, white pepper, black pepper, sumac, lemon juice, oil, and grated garlic.
Add the chicken legs and coat them thoroughly in the marinade.
Let the chicken marinate for at least 1 hour, or overnight for best flavor.
Preheat your oven to 180°C (350°F).
In a baking dish, scatter the cubed potatoes and onions.
Place the marinated chicken legs on top of the vegetables.
Pour 1/2 cup broth around the chicken (not directly on top).
Cover the tray tightly with foil.
Bake at 180°C for 45 mins covered with foil.
After 45 mins, remove the foil and continue baking until the chicken is golden and the potatoes are fully tender (about 20–25 minutes).
Plate the roasted chicken and potatoes with turmeric rice, your favorite pickles, and a drizzle of pomegranate molasses.
Optionally garnish with chopped parsley or an extra sprinkle of sumac.