Rinse and soak the chana dal in warm water for at least 1 hour.
Peel and roughly chop the onion. Peel the galagnal, garlic and trim the lemongrass. Add all of them into a food processor with the ground spices and pulse until a fine paste forms. Discard the tough stalks from the makrut lime leaves and thinly slice.
Place a saucepan on medium heat. Once hot, add half of the coconut milk and cook, stirring, until the oil separates and the coconut solids turn golden, 3-5 mins. Add the curry paste and toast for 2-3 mins. Then, add the drained chana dal, curry leaves, lime leaves and cook for 2-3 mins until fragrant. Stir through the remaining coconut milk and your water. Bring to the boil, turn the heat down to medium-low and simmer until the chana dal has softened and the oil has separated from the curry, 20–25 mins. Stir the tamarind paste through and season with fish sauce. Add a splash of water if the curry is too thick – it should be quite loose.
Spoon the curry into bowls and mop up with some roti or paratha.
