Prepare the walnut base:
Grind the walnuts in a food processor until they form a fine paste. Transfer to a large, heavy-based pot or Dutch oven, add 1 litre of water, and stir well to combine.

Simmer the sauce:
Bring the walnut mixture to a boil over high heat and allow to bubble vigorously for 5 minutes.
Then reduce the heat to low, partially cover, and let it simmer for 1 hour, stirring occasionally.

After the first hour, add another 200 ml of water, stir again, and continue simmering (covered) for another 1 hour. If the mixture becomes too thick or dry, add a splash of cold water as needed. The sauce should become thick, creamy, and dark brown.

Flavour the stew:
Stir in the pomegranate molasses, tomato purée, cinnamon, sugar, salt, and pepper.
Add the chicken thighs to the sauce, cover, and gently simmer for about 45 minutes, until the chicken is tender and the sauce has taken on a rich, chocolatey colour and silky texture.

Final adjustment:
Taste and adjust the seasoning — add more sugar for sweetness, or more pomegranate molasses for tartness.
Uncover and let the stew simmer for a final 10 minutes, to thicken slightly.

Serve:
Scatter with fresh pomegranate seeds and serve with steamed saffron rice.