Season your lamb shanks well with salt and pepper. Dust them lightly with a little bit of flour. This helps the meat brown and thickens the sauce later. Shake off any extra flour before cooking.

Heat oil in your large casserole dish over medium-high heat. Brown the lamb shanks on all sides until they look dark and crispy. Take them out and set them aside on a clean plate.

In the same pot, add the onions, carrots, and celery. Cook them for about five to eight minutes. You want them to become soft and slightly golden. This builds a sweet flavor base.

Stir in the minced garlic and the tomato purée. Cook this for just two minutes. Make sure you smell the garlic but do not let it burn. This adds a rich color to the gravy.

Pour in the red wine and stir well. Use your spoon to scrape up all the brown bits from the bottom. These bits are full of flavor. Let the wine bubble and reduce by half.

Pour the stock into the pot. Add the rosemary sprigs and the bay leaves. Put the browned lamb shanks back into the liquid. Ensure the meat is mostly covered by the tasty juices.

Cover the pot with a tight lid. Put it in the oven at 160°C or simmer very low on the stove. Let it cook for at least two and a half hours. The meat should be very tender.

Once the lamb is cooked, remove the meat and herbs. Boil the liquid on the stove for ten minutes. This thickens it into a glossy, rich sauce. Pour it over the lamb and serve.