Sago is made from tapioca starch and is sold as tiny “pearls”. You can buy them in two sizes, small and large: the small ones are used in desserts and some savory dishes that make the most of their starchy texture. I use large sago pearls for this recipe as they fluff up into separate grains whereas the small ones tend to disintegrate into a paste when soaked.
Wash the sago well then soak it in enough water to cover it by 1-inch. Leave for 1 hour, then drain through a sieve, spread out on a clean, dry kitchen towel, and leave on the kitchen counter to soften.
After 3 hours, the water should be completely absorbed. The draining time can vary depending on the quality of the sago; a sago pearl should squash easily between the thumb and index finger when it is ready to be cooked.
Mix the crushed peanuts, salt to season, and sugar into the sago. Set aside.
Heat the oil in a skillet over high heat and add the cumin seeds. Cook until they darken, then add the chiles and curry leaves (standing back from the pan if using fresh leaves, as they will splutter). Add the potato, season with salt, and cook for 4 to 5 minutes until golden. Reduce the heat and cook for 8 to 10 minutes until the potatoes are tender.
Add the sago. Cook over a very low heat, stirring, for 5 to 6 minutes until the sago is soft all the way through. Sprinkle with the coconut, cilantro leaves, and lemon juice and serve hot.