Wash the cashew nuts, then soak them in a bowl of water for a couple of hours. Chop the onion and chile. Remove the cashew nuts from the water, drain and place in a saucepan together with the chile, 1 tsp of curry powder, the turmeric, coconut milk, chile powder, salt, fenugreek and curry leaves. Bring to the boil and simmer for 5 minutes. Heat the oil in a frying pan and toss in the onion for a couple of minutes. Add the cashew nut mixture and cook for a further 3 4 minutes then sprinkle with remaining curry powder.