Add enough water to the fermented batter in a bowl to get dosa batter consistency.

Heat a non stick pan or iron tawa over high heat, add a drop of oil and rub half an onion on it. Once the tawa is heated, reduce the heat to medium and pour a ladle of batter in the centre.

Using the back of the ladle, spread the batter in a circular motion.

Drizzle a teaspoon of oil around the dosa and close it with a lid.

Once the edges start browning and the dosa is cooked, reduce the heat, add 2-3 tablespoons of potato masala and a little butter (optional).

Flatten the potato mixture slightly along the diameter of the dosa.

Using the spatula, carefully loosen dosa and fold the sides of the dosa around the filling to make a cylindrical shape.

Remove from the pan and serve immediately with chutney and sambar of your choice.

Continue making dosas one at a time.