Cut the preserved lemons in half and pop out any seeds, then pop them in a blender. There may not be any, but they are best removed.
Add the coriander, parsley, peeled garlic cloves, half of the salt, cumin, and chilli flakes to the blender, then pour over the olive oil.
Blend to a coarse and thick paste, adding more olive oil if required.
Heat a frying pan that can be transferred to the oven over a high heat, and when it is hot, add the cooking oil.
Season the chicken thighs with the remaining salt, then brown them skin side down in the oil.
When the skin is a nice golden colour, flip over the chicken and then sprinkle over the zaatar.
Spoon the chermoula sauce over the chicken thighs to create a coating 3-5mm thick over the skin.
Place in the oven and cook for 30-40 minutes at 180°C or 350°F, or until the chicken reaches an internal temperature of at least 73°C or 165°F. I prefer to cook chicken thighs on to around 80-85°C or 175-185°F.