To prepare the spices for the spice mix, grind using a pestle and mortar or coffee grinder and set aside
Heat the oil in a large, heavy-bottomed pan and add the cumin seeds, cloves, bay leaves, and garlic
Finely dice 2 of the onions and cut the other onion into thin rings. Once the garlic turns golden in colour, add the onion. Cook until the onions are soft
Once soft, add the diced lamb leg and cook until browned and half-cooked, for 10-15 minutes. Add the chilli powder and Rogan Josh spice paste
Stir well for another 5 minutes then add the yoghurt. Cook for another 20 minutes until the meat is tender
Add the vegetables, then slowly stir in the spice mix, cook for another 5-8 minutes. Check the seasoning and add the coriander leaves
Preheat the oven to 200°C/gas mark 6
Reheat the mashed potato in the microwave with a dash of water until piping hot. Stir in the turmeric (if using) and grated cheese until combined
Transfer the meat to a pie dish and top off with a layer of the mashed potatoes. Place in the oven for 10-12 minutes
Remove the shepherd's pie from the oven and divide onto plates. Serve immediately
