How to Make It
Preheat the oven to 325°. In a small skillet, simmer the curry paste with the fish sauce and 1/4 cup of the palm sugar over moderate heat, stirring occasionally, until the sugar is dissolved and a smooth paste forms. Let cool slightly.
Season the pork with salt and rub it all over with the curry paste. Set the roast in a large enameled cast-iron casserole. Cover and roast, basting occasionally with the pan juices, until the meat is very tender, about 3 1/2 hours. Uncover and roast until a golden-brown crust forms, about 15 minutes.
Transfer the pork to a large bowl and let rest for 15 minutes. Using 2 forks, shred the meat. Skim the fat from the pan juices, then stir the juices into the shredded pork. Cover with foil and keep warm.
Make a large double layer of foil. Wrap the cilantro stems, garlic, shallots, lime leaves, chile, lemongrass, ginger, cardamom and turmeric in the foil and seal the sides. Set the packet seam side up directly on a burner or in a cast-iron skillet. Cook over moderate heat until aromatic and beginning to smoke, about 5 minutes. Using tongs, transfer the packet to a rack; let cool slightly. The cilantro stems should be tender and the ingredients on the bottom should be lightly charred.
Scrape the contents of the packet into a food processor. Add the remaining 2 tablespoons of palm sugar and process to a smooth paste.
Open the can of coconut milk and spoon the thick cream on the surface into a large saucepan. Bring to a simmer over moderately high heat and whisk in the cilantro paste. Whisk in the coconut milk and chicken stock and bring to a simmer. Stir in the pulled pork and season with salt and pepper. Cook until the sauce has thickened slightly, about 10 minutes. Stir in the chopped herbs and season with salt and pepper. Keep warm.
Spread mayonnaise on the buns and top with the pulled pork, cucumber, red onion, cilantro and basil leaves. Serve with lime wedges.