Soak the black gram and fenugreek in water until soft. Chop the onion and chile. Drain the gram and fenugreek and liquidize with the rice flour, rice and sufficient water to make a batter. Add the salt and turmeric. Heat 25 ml oil and fry onion, chile, curry leaves and cumin, then add to the batter. Reheat the pan, add a little oil and pour in batter to make a thin pancake. When little holes appear on the thosai turn it over and cook on the other side for a minute or two. Repeat process until all the batter is used up.