Put the potatoes in a saucepan and cover with cold water. Add the turmeric and salt. Bring to the boil, then turn down to simmer and cook for 15–20 minutes, until the potatoes are just tender enough to insert a fork. Drain well.
In a large frying pan over a high heat, heat the 2 tablespoons of oil. When the oil is shimmering, add the potatoes. With a fork, gently press down on each potato, breaking the skin and smashing them a bit. You don’t want to break them up, just smush them up a little. Cook for 2–3 minutes and when they are nice and golden brown, turn each potato over. When they are brown on both sides, transfer to a bowl while you make the temper.
Pour 2 tablespoons of oil into the frying pan. When hot, add the onion and cook until it starts to go translucent.
Add the curry leaves, garlic, green chilli, Maldive fish and pandan leaf, if using. Stir-fry for 2–3 minutes, until the curry leaves are bright green. Add the chilli powder or dried red chillies, mustard seeds and add a little more oil if necessary to keep everything bright and moving. After 1–2 minutes, when the seeds start to pop, return the potatoes to the pan and stir through, coating thoroughly in the spicy mixture. Finish with a squeeze of lime juice.
