Bring a large pan of water to the boil over a medium-high heat and cook the potatoes for 10-15 mins until just tender (a cutlery knife should just be able to cut through). Drain and set aside.

Heat the oil in a large frying pan over a low heat and add the mustard seeds. When they begin to pop, add the curry leaves, chilli, garlic and ginger, and cook for 1 min until the aromas start to release. Stir in the tomatoes, then cover and cook for 10 mins until soft and mushy

Add the garam masala, chilli powder, turmeric and 1 tsp salt. Mix well and cook for another minute before adding the cooked potatoes. Pour in 200ml water, cover and simmer for 10 mins until the potatoes are completely tender. Mash a few of the potatoes with a potato masher, keeping the rest whole. Sprinkle over the coriander leaves to serve.