Heat the oven to 220C. Put the first six ingredients in a blender with a teaspoon and a half of salt and blitz smooth. Arrange the squash slices in a round, 28cm cast-iron pan or baking dish, then pour over the curry coconut milk mixture.
In a small bowl, mix the coconut flakes with the maple syrup and a good pinch of salt, and set aside.
Cover the cast-iron pan or dish with foil, bake for 60 minutes, then remove the foil, drizzle over the oil, cover with the coconut flake mix and bake for 10 minutes more. Turn the oven to a high grill setting, then grill for four or five minutes, until nicely browned on top.
While the gratin is baking, make the topping. Put the oil in a small saucepan on a medium-high heat. Once hot, add the chilli and fry for 90 seconds, swirling the pan so it doesn’t catch, then add the curry leaves and fry for another 30 seconds, until the leaves are crisp (careful, they might spit). Strain the chilli and curry leaves through a sieve set over a heatproof bowl to collect the oil.
Drizzle the aromatic oil and the reserved two tablespoons of coconut milk over the gratin, then sprinkle on the chilli and curry leaves and serve with the lime wedges for squeezing over.
