How to Make It
Put the pork in a large, resealable plastic bag. In a small bowl, combine the crushed red pepper, cracked black pepper, coriander, sugar and 1 tablespoon of salt. Add the mixture to the bag, seal and shake to evenly coat the pork. Refrigerate overnight.
Preheat the oven to 325°. Transfer the pork to a small roasting pan and roast for about 2 hours and 15 minutes, until an instant-read thermometer inserted in the thickest part of the meat registers 185°. Let the pork rest for 20 minutes.
Meanwhile, in a large nonstick skillet, heat the olive oil. Add the mushrooms and onion and season lightly with salt. Cover and cook over moderately high heat, stirring once or twice, until the onion is softened, about 5 minutes. Uncover and cook, stirring occasionally, until the shiitake are tender and browned, about 5 minutes longer. Add the vinegar and cook until nearly evaporated. Stir in the butter and chives and keep warm.
Slice the pork and serve with the mushrooms.