Preheat your oven to 325°F (160°C). Season the lamb shanks generously with salt and pepper.

In a large Dutch oven, heat olive oil over medium-high heat. Brown the lamb shanks on all sides, about 4–5 minutes per side. Transfer to a plate.

Reduce heat to medium, add onions and garlic. Sauté until translucent, about 5 minutes.

Stir in diced tomatoes, red wine, and broth, scraping up any browned bits from the bottom.

Return lamb shanks to the pot and nestle in rosemary sprigs and bay leaf.

Bring liquid to a gentle simmer, then cover and transfer to the oven. Braise for 2½ to 3 hours, or until meat is tender and falling off the bone.

Remove lid for the last 30 minutes to thicken the sauce.

Discard rosemary sprigs and bay leaf. Taste and adjust seasoning.

For extra depth, swirl in a pat of butter just before serving.

Serve hot over creamy mashed potatoes or polenta. Garnish with fresh rosemary.