In a small dry pan, toast the fenugreek seeds over medium heat for 2-3 minutes until fragrant and lightly golden. Set aside to cool, then lightly crush using a mortar and pestle.

In a large bowl, combine the lamb cubes with half the garlic, half the ginger, vinegar, chilli powder, cumin, ground coriander, turmeric, and cinnamon. Mix well and marinate for 15 minutes.

Heat the vegetable oil in a large heavy-bottomed pot or Dutch oven over medium-high heat. Working in batches, brown the lamb pieces on all sides for about 5 minutes per batch. Remove and set aside.

In the same pot, add the sliced onions and cook for 8-10 minutes until deeply golden and caramelised. Add the remaining garlic, ginger, cloves, and peppercorns. Sauté for 2 minutes until fragrant.

Return the lamb to the pot along with any marinade. Add the chopped tomatoes, stock, brown sugar, and three-quarters of the toasted fenugreek seeds. Stir well to combine.

Bring to a boil, then reduce heat to low. Cover and simmer for 70-80 minutes, stirring occasionally, until the lamb is fork-tender and the internal temperature reaches at least 75°C when checked with a meat thermometer.

In the final 10 minutes of cooking, stir in the fresh mustard greens and allow them to wilt into the curry. Adjust salt to taste.

Serve the vindaloo garnished with the remaining roasted fenugreek seeds and fresh coriander leaves. Accompany with steamed basmati rice or warm naan bread.