Remove the first layer of skin from the onions and finely chop them.
Wash the celery stalk and cut it into pieces.
Use a garlic press to extract the pulp from the garlic clove.
Heat a non-stick skillet over medium heat with 2 tablespoons of oil. Sauté the garlic, onions, celery, turmeric, ginger, and salt for 5 minutes, stirring regularly.
Heat another skillet with 2 tablespoons of oil and the butter over high heat. Brown the chicken thighs on all sides for 5 minutes.
Cut the preserved lemon into quarters. Remove the pulp and chop the skin. Slice the organic lemon into rounds.
Put the saffron threads in 6.76 fl oz of hot water.
Place the garlic, onions, and celery at the bottom of a tagine dish. Lay the chicken thighs on top. Add the lemon slices, preserved lemon, and olives. Pour the saffron-infused water over everything. Cover the tagine.
Bake at 356°F (180°C) for 20 minutes. Uncover and continue cooking for 10 minutes.
Garnish the tagine with cilantro leaves.