Preparation:
Preheat oven to 350°F.
In a 9-quart heavy ovenproof kettle cook sugar on top of stove over moderate heat, without stirring, until it begins to melt. Continue to cook sugar, stirring with a fork until melted and cook without stirring, swirling kettle, until a deep golden caramel. Add vinegar and stir until caramel is dissolved. Stir in tomatoes with juice, wine, rosemary, cinnamon, and bay leaf and bring to a boil. Add lamb shanks and braise, covered in middle of oven until tender, about 2 hours. Braised lamb shanks improve in flavor if made 1 day ahead. Cool mixture, uncovered and chill, covered. Skim and discard fat from mixture and reheat on top of stove before proceeding.

In a saucepan of boiling water blanch onions 10 minutes, or until just tender, and drain. Cool onions and peel.

Quarter potatoes and in a steamer set over simmering water steam potatoes, covered, 8 to 10 minutes, or until just tender. In a large non-stick skillet cook garlic in oil over moderate heat, stirring, until pale golden. Add potatoes with salt and pepper to taste and sauté mixture over moderately high heat 5 minutes, or until potatoes are golden.
Transfer meat with a slotted spoon to a platter. Discard cinnamon stick and bay leaf. Add onions to sauce and boil until sauce is thickened slightly. Spoon sauce and onions over meat and surround with potatoes.

Serves 4.