The marinade for this dish is based on my favourite recipe from the Indian vegetarian cookbook Dakshin by Chandra Padmanabhan (Periplus Editions, 1999). The longer you cook the ribs, the more the rich tamarind paste develops in flavour. After 24 hours the meat is nicely cooked, but after 48 hours the flavours have melded and the lamb is meltingly tender. Ask your butcher to cut the ribs for you when they get their lambs in.