Season and sear the shanks: Pat the 6 lamb shanks completely dry and season all over with 2 teaspoons salt and 1 tablespoons black pepper, ground. Heat 3 tablespoons olive oil in a heavy-based casserole or Dutch oven over high heat and sear the shanks in batches until deeply browned on all sides, about 3-4 minutes per side. Don't crowd the pan — this browning is where most of the flavour comes from. Remove and set aside.
Build the base: Lower the heat to medium and add the 2 medium onions, finely diced to the same pot, scraping up any browned bits. Cook until soft and golden, about 8 minutes 08:00. Add the 4 garlic cloves, crushed and cook for 1 minute more, until fragrant.
Deglaze with wine: Pour in the 500ml dry white wine and bring to a boil, scraping the base of the pot well. Let it reduce by roughly half — this concentrates the flavour and cooks off the raw alcohol.
Add tomato, coriander and stock: Stir in the 250ml tomato paste, chopped 4 tablespoons fresh coriander, chopped (plus extra to finish), and ground coriander seed 1 teaspoons ground coriander seed. Return the shanks to the pot along with the 300 ml lamb or chicken stock, making sure the liquid comes about two-thirds up the shanks. Bring to a gentle simmer.
Braise low and slow: Cover and transfer to a 150°C (300°F) oven, or keep on the lowest stovetop simmer. Cook until the meat is falling-away tender and pulls easily from the bone.
Reduce and finish: Lift the shanks out onto a warm plate. If the sauce is thin, simmer it uncovered on the stovetop for 10 minutes 10:00 until glossy and coating the back of a spoon. Check seasoning, stir through the 1 lemon, zested, return the shanks to coat, and finish with extra fresh coriander.
Note:Modern touches vs. the original: searing the shanks properly before braising (rather than frying everything together) builds a deep fond; deglazing and reducing the wine separately concentrates flavour instead of diluting it; a low, covered oven braise gives more even, hands-off tenderness than stovetop simmering; and finishing with lemon zest and fresh herbs lifts the richness of an expensive cut so none of it goes to waste.