Preheat oven to 350 degrees Fahrenheit.
Season pork with salt, pepper, and paprika. In a large cast iron pot, heat 1 tablespoon grapeseed oil over medium heat. Add pork, fatty side down, and cook, turning each side until all sides are browned (about 10 minutes).
Remove pork from the pot and add the onion. Cook until golden about 3 minutes, then add garlic, cooking for an additional 30 seconds. Add tomatoes to the pot and season with more salt and pepper. Add broth and red wine vinegar. Cook, stirring and scraping up browned bits from the bottom of the pan.
Return pork to pot ( leaving the tomatoes and broth still in the pot). Bring the roast to a boil over high on the stove top. Once the pork has come to a boil, cover, and transfer to oven; cooking for one hour.
Remove the pot from the oven, and carefully turn the pork. Return back to the oven and cook covered for an additional hour. Using a meat thermometer make sure the internal temperature of the pork reaches at the very minimum 145 degrees.
Transfer pork to a cutting board and let it rest for 15 minutes.
While the pork rest, bring the liquid to a boil. Whisk together the cornstarch and ½ cup of the liquid. Stir in the cornstarch slurry and cook until sauce is thick. Slice pork and serve with gravy.