Gather and prepare the ingredients.
Wash and prepare the chicken. The chicken is usually cooked whole, but check the size of your tagine and make sure it will fit. You can cut the chicken in half (long ways) or quarters if it makes it easier.
Peel and wash the potatoes, then slice them into quarters long ways.
Remove the inside of the preserved lemons and chop it finely. Save the skin for cooking.
Add all the herbs and spices with the lemon and oil to a large mixing bowl along with the onion and garlic, and mix it all together to form a marinade. Also, add the saffron and smen if you are using it.
Then add the chicken to the mixing bowl and smother it all with the Moroccan chicken marinade. Cover and let the chicken marinate in the refrigerator for at least 2 hours preferably overnight, before cooking.
Add some olive oil to the bottom of the tagine and place the marinated chicken in it, (breast side up), arrange the rest of the onions and marinade all around it.
Add the olives and reserved rind of the preserved lemons, and drizzle any remaining olive oil over the chicken.
Add the water to the tagine, cover, and place on a heat diffuser over medium-low heat.
Give the tagine time to reach a simmer without taking off the lid. If you don't hear the tagine simmering within 20 minutes, slightly increase the heat, and then use the lowest heat setting required for maintaining a gentle simmer. (this may depend on the strength/power of your cooker stove.
Allow the chicken to cook like this undisturbed for about 1hr. Then take the chicken out and place on a lined baking tray to roast in the oven until golden and crispy.
Meanwhile, place the potato quarters over the tagine gravy, add a little bit more water if needed and cover the tagine again to allow the potatoes to cook. (This may take between 20-30)
Arrange the chicken over the Tagine sauce and decorate it with some preserved lemon, potatoes and olives.
Enjoy hot with some freshly baked Moroccan bread