How to Make It
Season the pork with the 2 teaspoons of salt and 1 teaspoon of pepper. Heat a large cast-iron casserole over moderately high heat. Add the pork, fat side down, and add 1/2 cup of water. Cook until all of the water has evaporated, about 5 minutes. Continue to cook over moderate heat until the pork is golden brown, about 8 minutes. Flip the pork and cook, turning occasionally, until browned all over, about 5 minutes longer.
Add the onion and garlic to the casserole and cook, stirring occasionally, until lightly golden, about 5 minutes. Add the stock, wine and parsley and thyme sprigs and bring to a simmer. Cover and cook over low heat, turning once, until the pork is just tender, 2 1/2 hours. Add the sweet potatoes and chestnuts, cover and cook until the pork and sweet potatoes are very tender, 30 minutes.
Transfer the pork to a cutting board and let rest for 10 minutes. Using a slotted spoon, transfer the sweet potatoes and chestnuts to a platter. Strain the jus into a bowl and degrease with a spoon; season with salt and pepper.
Slice the pork and arrange it on top of the vegetables. Garnish with parsley and serve with the jus.