Stir the saffron into the warm water in a small bowl and leave to stand for 5–10 minutes.
Place the chicken in the base of a large tagine. Rub the salt all over the chicken.
Combine the olive oil, lemon juice and orange blossom water in a bowl. Add the saffron water and stir in most of the chopped herbs, then pour the mixture over the chicken.
Cover and place the tagine in a preheated oven, 180°C (350°F), Gas Mark 4, for 1 hour, basting the chicken with the cooking juices from time to time.
Scatter the butter over the chicken, then return to the oven, uncovered, for 15 minutes until the chicken browns lightly on top. Garnish with the remaining parsley, mint, and dill and serve with couscous and a salad, if liked.