1 Heat the butter in a deep pan and fry the sliced onions until brown and crisp. Remove from the pan, drain on kitchen paper and set aside.
2 Put the chopped onions, ginger, garlic, chile peppers, cloves, cardamom pods, cinnamon and lime juice in a food processor and blend briefly to make a coarse puree.
3 Rub the onion puree into the beef and set aside to marinate for 1 hour.
4 Heat the pan with the butter used to cook the sliced onions and add the beef and the marinade. Fry until the meat is browned on all sides then add about 1 cup of water, salt and pepper and simmer very, very gently with a lid on for about 1 hour or until the meat is very tender. Add a little more water during the cooking if needed to prevent the dish burning.
5 While the meat is cooking, cook the rice according to the packet instructions. Dissolve the saffron strands in a little hot water and stir into half the rice. Mix the saffron rice into the white rice.
6 Serve the meat and its sauce with the rice, scatter over the fried onions and garnish with mint leaves.