Heat the oven (with the oven rack in the middle) to 300°F.
In a large Dutch oven or heavy bottomed ovenproof pot, heat the oil over medium-high heat. Season the roast with 1½ teaspoons of the salt and the pepper. Add to the pot and cook until well browned on all sides, 10 to 12 minutes total.
Meanwhile, slice the onion, carrots, parsnips, and celery. Smash the garlic.
Transfer the roast to a plate. Add the vegetables and garlic to the pot and cook, stirring often, for about 5 minutes, or until they just start to brown.
Stir in the tomato paste and cook, stirring, for 1 minute.
Add the wine, thyme, 1 cup water, and the remaining ½ teaspoon salt and stir to combine.
Nestle the roast into the vegetables. Cover tightly and transfer to the oven.
Roast 2½ to 3 hours, until the roast is fork tender.
Using two forks, pull the meat apart into large pieces and serve with the vegetables and sauce.
