Peel the zest from the lemon, then cut into strips, finely chop and set aside. Now cut the lemon in two, squeeze its juice into a bowl with the saffron and mix together. Fry the sliced onions in the oil until soft and starting to colour, then add the coriander, cumin and lemon zest and cook for 1 min more. Remove from the heat, stir in the cranberries, nuts, couscous and chopped parsley, then season well. When cool, beat in the eggs.
Wash and dry the turkey, removing any feathers with tweezers. Pull out the giblets and neck and discard, or use to make stock for the gravy. Lift up the skin that covers the neck opening, then push some stuffing into the cavity, packing it in well. Secure tightly underneath with a skewer or two cocktail sticks. Shape the rest of the stuffing firmly into balls and chill until ready to bake. Put the onion quarters in the turkey cavity with any leftover stalks from the parsley. Can chill at this stage up to 1 day ahead.
Heat oven to 190C/fan 170C/gas 5. Weigh the stuffed turkey and calculate the cooking time, allowing 40 mins per kg (20 mins per lb). Put the turkey in a roasting tin. Mix the butter with the saffron mixture and brush generously onto the turkey. Pour 500ml water into the tin, then roast for 1 hr. Brush with the buttery mixture again, then loosely cover with foil and roast until 15 mins before the time is up. Mix the honey into the remaining buttery mix, brush over the turkey and cook uncovered for 15 mins more until golden.
Pierce the turkey thigh through its thickest part – the juices should run clear. If not, return to the oven for another 20 mins and test again. Leave to rest on a platter, covered with a clean tea towel. Reserve the juices in the roasting tin to make the gravy.
Meanwhile, twist the sausages in half and snip to separate. Toss with the harissa, oil and onions in another roasting tin, then roast for 1 hr until golden. After 40 mins roasting, add the stuffing balls to the tin.
To make the gravy, drain the juices from the tin into a jug and skim off the excess oil. Put the roasting tin over heat, pour in the stock and loosen the savoury bits on the base with a wooden spoon. Add any juices from the resting bird to the mixture along with the onions from the sausages, then simmer for about 10 mins. Blitz with a hand blender until smooth and thick. Taste and season, or add a little redcurrant jelly to sweeten, if you like.
To serve, put the turkey on a platter and surround with the sausages and stuffing balls. Garnish with parsley sprigs and bay.