Season the pork with salt and pepper and brown over high heat, 3-4 minutes per side.
Transfer to an enameled cast iron casserole and add the garlic, onions, thyme, bay leaf, stock and 2 cups of water; bring to a boil.
Cover with foil and bake for 2 1/2 hours, until the pork is falling apart tender.
Transfer to a dish and keep warm.
Strain the liquid, return to the casserole and reduce by half over moderately high heat.
Season with salt and pepper, add to the pork and serve with chimichurri.
Note: Use store-bought chimichurri or make Animal's excellent version. In a mortar mash one chopped garlic clove with one seeded jalapeno. Season with 1 tsp salt. Work in one bunch each of stemmed curly and flat leaf parsley and 1/4 cup of chopped oregano. Stir in 3/4 cup of olive oil and 2 Tbs of white wine vinegar and season with 1/2 tsp of crushed red pepper.