How to Make It
In a very large pot, whisk the kosher salt and brown sugar with 6 quarts of water until dissolved. Wrap the árbol chiles, oregano, garlic, bay leaves, star anise and 1 tablespoon of the fennel seeds in cheesecloth and tie the bundle with kitchen twine; add to the brine.
Submerge the pork in the brine, cover and refrigerate overnight.
In a medium saucepan, combine the coriander, cumin and the remaining 1 tablespoon of fennel seeds. Toast over moderately high heat until fragrant and just starting to brown, about 3 minutes. Transfer to a spice grinder; let cool, then grind to a powder. In a small bowl, whisk the oil with the spices, Thai chiles, vinegar and 1 1/2 teaspoons of sea salt.
Remove the pork from the brine and pat dry. Put the pork on a rack set over a large rimmed baking sheet. Rub the seasoning mixture all over the meat and shape it into a tight roast. Refrigerate uncovered overnight. Let the pork stand at room temperature for 30 minutes before roasting.
Preheat the oven to 425°. Roast the pork until well browned, about 45 minutes. Remove the pork from the oven and reduce the oven temperature to 350°. Lay 2 very large sheets of heavy-duty foil on a work surface, set the pork in the center and wrap up tightly. Return the pork to the rack and roast until very tender, about 2 hours longer. Let rest in the foil for 30 minutes.
Unwrap the pork and transfer to a carving board. Thinly slice against the grain. Pile the sliced pork and the slaw on the dinner rolls, slather with aioli and serve.