Oil a plate, that has a 2.5-cm / 1-inch rim with 1 teaspoon oil and set aside.
Whisk the yoghurt with 250ml / 8fl oz (1 cup) water in a bowl.
Add the rice flour, a spoonful at a time, beating well between each addition to make a smooth batter without any lumps. Season with salt and stir in the coriander leaves.
Heat the 2 tablespoons oil for the tempering in a kadhai or deep, heavy-based frying pan (skillet), add the mustard seeds, asafoetida, chilies, urad dal, and curry leaves, and stir-fry for 1 minute, or until the mustard seeds start spluttering.
Pour in 250 ml / 8fl oz (1 cup) water and bring to boil over high heat. Reduce the heat, then pour in the batter and cook over low heat for 5-7 minutes, or until the water is almost absorbed, stirring constantly to prevent lumps.
Add 4 tablespoons oil and keep stirring until the mixture leaves the sides of the pan. Pour onto the oiled plate, flatten with a spatula and allow to cool.
Cut into diamond-shaped pieces before serving.