JUS: Place first 6 ingredients in a saucepan, bring to boil and cook, uncovered, until reduced by half. Strain through a sieve and add chopped coriander.
Season to taste with salt and pepper. Set aside.
VEGETABLES: Place tomatoes on a baking sheet and sprinkle lightly with oil, vinegar, salt and sugar. Roast at 130 ºC for about 1 hour, or until soft and slightly browned.
Wash spinach well and steam until wilted, adding a dash of jus, or season with salt, pepper and nutmeg.
COUSCOUS: Bring water, salt, saffron and stock to boil. Boil for about 5 minutes. Pour over couscous, cover and leave until couscous is swollen and fluffy. Drain, if necessary.
TO ASSEMBLE: Use individual moulds (ramekins) and tip out, or shape by hand.
If using ramekins, layer as follows: couscous, tomatoes, spinach and turn out onto plates.
If shaping by hand, start with a layer of spinach, top with tomatoes and spoon couscous over.
If desired, deep-fry thin slices of leek (white parts only) and arrange on top. Heat jus and pour around couscous tower, then serve.
Serves 10-12 as starter or 4-6 as a main course.