Preheat the oven to 350°F (180°C) (without fan).

Heat the oil in a large oven-proof pot which will fit all of the ingredients comfortably.

Sear the lamb shanks in batches until they are golden brown on all sides.

While you are searing the lamb shanks, place the onion, celery and garlic into a food processor until finely chopped.

Remove the lamb shanks to a plate.

Turn down the heat. If the pan is really hot, remove it from the stove and let it cool a little.

Add the onion mixture and cook for a few minutes until the vegetables have softenend.

Stir in the tomato paste and cook for a few more minutes.

Add the red wine and let the mixture bubble away for a few minutes to allow the alcohol to cook off.

Add the canned tomatoes, stock, sugar, bay leaves, and orange peel.

Bring the mixture to a boil and let it simmer gently for a few minutes.

Return the lamb shanks to the pan, together with any meat juices on the plate. Make sure the shanks are well-submerged in the sauce.

Place the lid on the pan, and place the pan into the oven for 2 hours to braise. Check the pan every 30 minutes or so to give it a stir.

After 2 hours, place the pan back on the stove on low heat. Remove the lid.

Skim off and discard as much fat as you can from the sauce.

At this stage, the sauce should look quite thin.

Let everything simmer gently, without the lid, for about 1 hour, or until the sauce has thickened nicely and the meat is very tender.

Stir the sauce occasionally to make sure that it is not sticking to the bottom of the pan.

Taste the sauce for seasoning, and add salt and pepper. If it tastes too tart or sour, you might need more sugar.

Make the gremolata by mixing together the parsley, garlic and lemon zest.

There are several ways to serve this dish. If the lamb shanks are quite small, I would serve one lamb shank per person. Alternatively, you could pull the meat from the bones, and either serve the meat in large chunks or roughly shredded and mixed through the sauce. The latter is a good option for leftovers.

Serve the lamb shanks with risoni pasta, mashed potatoes, or polenta.

Sprinkle generously with gremolata just before serving.

If you plan to serve this dish with pasta (whether risoni pasta or another type of pasta), I would recommend warming the pasta through the sauce first. To do so, simply remove a few ladelfuls of sauce (or enough to serve with the pasta) into a medium saucepan and bring to the boil. Add the cooked and drained pasta, and stir everything together over high heat until the pasta is flavoured with the sauce. Alternatively, you can serve the pasta separately at the table, but this should be done as soon as the pasta is cooked and drained.