First prepare the filling. Grind the coconut and chillies to a powder in a coffee or spice mill. Transfer the mixture to a small bowl and add the cumin, ground coriander, salt, lemon juice and 60 ml (2 fl oz) water. Mix and set aside.
Heat the oil in a non-stick saucepan over low heat. Add the mustard seeds, then as soon as they start crackling, stir in the turmeric.
Add the potatoes and the coconut mixture. Stir until the potatoes are heated through and the liquid is completely absorbed. Stir in the chopped coriander leaves, then keep the filling hot over very low heat while you make the pancakes.
In a large mixing bowl mix the semolina, ground rice, flour and salt. Mix the yogurt with 375ml (13 fl oz) water, then gradually add to the semolina mixture, whisking well with a wire whisk. Alternatively, put all the ingredients in a blender or food processor and blend until smooth.
Heat a large, heavy griddle or non-stick frying pan, at least 23cm (9in) in diameter, over medium heat and brush the surface lightly with oil. Wait until the surface of the pan is really hot, then pour about 125m1 (4 1/2 fl oz) batter from a measuring jug, spreading it quickly and evenly on the pan. Allow the mixture to cook and set for 2 minutes.
Sprinkle 1 tablespoon water around the edges, wait for 15-20 seconds, then turn the dosa over with a thin spatula or a fish slice. Cook for a further 2-3 minutes or until brown patches show through underneath.
Place a little of the spiced potato mixture on top and roll it up. Keep hot until the remainder of the batter is cooked. Serve immediately, with Almond Chutney.
1 tablespoon desiccated coconut
2-4 dried red chillies, broken up
1 teaspoon Ground Roasted Cumin
1 teaspoon Ground Roasted Coriander
1 teaspoon salt or to taste
2 teaspoons lemon juice
1 tablespoon sunflower or soya oil
1/2 teaspoon black mustard seeds
1/2 teaspoon ground turmeric
550 g (1 1/4 lb) new potatoes, boiled and cut into bite-sized pieces
2 tablespoons chopped fresh coriander leaves