Combine onion, oil, pepper, saffron, cinnamon and ginger in large bowl; add beef, toss to coat in mixture. Place beef in large deep saucepan with butter, undrained tomatoes the water, half of the sugar and 1/2 cup of the nuts; bring to boil. Reduce heat; simmer, covered, 1 1/2 hours. Remove 1 cup cooking liquid; reserve. Simmer tagine, uncovered, 30 minutes. Meanwhile, place prunes in small bowl, cover with boiling water; stand 20 mins, drain. Place prunes in small saucepan with rind, extra cinnamon, remaining sugar and reserved cooking liquid; bring to boil. Reduce heat; simmer, uncovered, about 15 minutes or until prunes soften. Stir into tagine. Make couscous. Divide couscous and tagine among serving plates; sprinkle tagine with remaining nuts.

Combine couscous with boiling water in large heatproof bowl, cover; stand for about 5 mins or until water is absorbed, fluffing with fork occasionally. Stir in spinach.