Plain and masala dosa from readymade dosa batter, with potato filling

For the filling, heat oil over medium heat; lower the heat, add black mustard seeds and cumin seeds and let them splutter.

Add a few chana dal and stir until golden brown, then a few curry leaves.

Add the onions with a sprinkle of salt and cook until just pale, not browned.

Add turmeric powder and stir a second; crumble in the boiled potatoes by hand.

Add a few tablespoons of water, salt and optional crushed red chili flakes; add two more tablespoons of water if dry and stir well.

Finish with a sprinkle of lemon juice. The filling keeps two to three days ahead.

Check the use-by date; mix the batter well because the solids settle, and thin it with a few tablespoons of water for a thin, crispy dosa. Return any unused batter to the fridge at once.

Wipe a drop of oil over the pan with a paper towel and heat over medium-high until very hot; sprinkle water -- the beads should evaporate in seconds -- which also brings the temperature down.

Turn the heat to the lowest mark, add about two ladlefuls of batter and spread it from the center outward in a circular motion without pressing.

Oil around the edges and fry on medium-low; do not lift until brown circles appear on top, then loosen gently from an edge with a spatula without forcing.

Roll it: this is a plain dosa.

For masala dosa, reheat the pan without oil, sprinkle water to cool it, wipe with a paper towel, lower the heat and spread the batter the same way.

When dark circles show, loosen the sides, add potato filling and roll; wipe the pan clean between dosas.

Variation: fill with cabbage curry from an earlier episode instead of potato.

Serve with the sambar and chutney.