Bring a large pot of salted water to a boil. Cook the pasta until just al dente, about 1 minute less than the package says. Reserve 1 cup (240ml) of the cooking water, then drain.

Meanwhile, heat the oil in a large, deep skillet over medium heat. Add the curry paste and stir constantly for 2 minutes, until it darkens a shade, the oil turns red, and the smell turns toasted rather than raw.

Add the garlic and ginger and stir for 30 seconds, until fragrant.

Shake the can of coconut milk well, then pour it in, scraping the bottom of the pan. Add the fish sauce and sugar. Simmer gently for 6 to 8 minutes, stirring occasionally, until the sauce thickens enough to coat the back of a spoon.

Add the drained pasta and toss for 1 minute. Add reserved pasta water, 1/4 cup (60ml) at a time, stirring until the sauce looks glossy and clings to the noodles rather than pooling.

Turn the heat to low. Gently fold in the crab with a spatula, trying not to break up the lumps, and warm for 1 minute until just heated through.

Remove from the heat. Stir in the lime juice, taste, and adjust with more fish sauce, sugar, or lime.

Divide among bowls and top with scallions, cilantro, chili, and lime wedges. Serve immediately.