Heat oil in a large deep frying pan or Dutch oven over medium heat until hot. Add the cumin seeds, onion, garlic, ginger and a 1/2 teaspoon of the salt and cook for, stirring often, for 10 minutes until soft and sweet.
Stir in the curry powder, ground coriander, cumin, and chilli powder and cook for 1 minute. Add the diced tomatoes and cook for about 8-10 minutes, stirring occasionally, until the tomato is pulpy.
Season the chicken with the remainder of the salt and add to the tomato mixture along with the potatoes and yoghurt. Stir through so that it's completely coated then add the water. Bring to a boil, then reduce heat to low, cover with a lid, and simmer for 20 minutes, stirring occasionally. Remove the lid and continue cooking curry for a further 10 minutes or until the potatoes are tender and the sauce has reduced and thickened.
Stir through the thickened cream, coriander and garam masala. Simmer for a further 1 minute. Serve hot curry with steamed basmati rice and naan or roti bread. Garnish with coriander sprigs or micro-greens.