Infuse the saffron
Stir the saffron threads into the hot chicken stock and set aside to infuse while preparing the other ingredients.
Brown the chicken
Select the Sauté function on the pressure cooker and heat the olive oil. Brown the chicken thighs in batches until lightly golden on both sides, then transfer them to a plate.
Soften the onions
Add the chopped onions to the pot and cook, stirring from time to time, until soft and beginning to caramelise.
Toast the spices
Stir in the sliced garlic, ground ginger, cumin and turmeric. Cook briefly until fragrant.
Assemble the tagine
Return the browned chicken to the pot. Add the cinnamon stick, saffron-infused stock, chopped preserved lemon and black pepper, then stir gently.
Pressure cook
Secure the lid and set the steam release valve to Sealing. Cook on High Pressure for 15 minutes.
Steam the couscous
Place the couscous in a heatproof bowl with the salt and the olive oil or butter, if using. Pour over the boiling water, cover tightly and leave to steam.
Fluff the couscous
Remove the cover and separate the couscous grains with a fork before serving.
Release the pressure
When pressure cooking finishes, allow the pressure to release naturally for 10 minutes, then carefully release any pressure that remains.
Reduce the sauce
Open the lid and remove the cinnamon stick. Stir in the green olives, select Sauté and simmer without the lid until the sauce has reduced slightly.
Add the herbs
Stir in most of the chopped coriander and parsley, keeping a little back for garnish. Taste before adding salt because the preserved lemons and olives may already provide enough seasoning.
Serve
Spoon the chicken tagine over or alongside the couscous, scatter over the reserved herbs and serve immediately.