Check the batter is the right consistency – it should be easy to spread, like crêpe batter, so add a little more water, if needed. Heat a few drops of oil in a large, non-stick frying pan over a medium heat and carefully wipe the oil around the pan using kitchen paper. Pour a ladle of batter into the pan and use the bottom of the ladle to spread it over the base, making a large, thin dosa. Drizzle 1 tsp oil around the edge of the dosa and turn up the heat. Cook until it turns golden and releases from the pan. Fold the dosa in half and remove from the pan. Repeat with the remaining batter.