Arrange a rack in the lower third of the oven and heat the oven to 350°F.

Cook 4 ounces diced pancetta in a Dutch oven or heavy-bottomed pot over medium heat, stirring occasionally, until lightly browned, 6 to 8 minutes. Meanwhile, pat boneless beef chuck roast dry with paper towels. Season all over with 2 teaspoons of kosher salt and ½ teaspoon black pepper.

When the pancetta is ready, use a slotted spoon to transfer it to a large plate. Add the roast to the pot and sear until well-browned on 2 sides, 3 to 4 minutes per side. Transfer to the plate with the pancetta.

Add diced yellow onion, diced carrots, diced celery stalks, minced garlic, and the remaining 1 teaspoon kosher salt. Cook, stirring occasionally, until the onions are softened, 5 to 8 minutes. Stir in dry red wine and bring to a boil. Boil for 1 to 2 minutes.

Stir in the reserved pancetta, low-sodium beef broth, crushed tomatoes, dried bay leaves, fresh thyme sprigs, and fresh rosemary sprig. Bring to a simmer. Return the roast and any accumulated juices to the pot.

Cover and transfer to the oven. Cook until the meat is very tender and gently falling apart when pricked with a fork, 3 to 3 ½ hours.

Skim off some of the fat from the surface if desired. Remove and discard the bay leaves, thyme sprigs, and rosemary sprig. Shred the roast into bite-size pieces right in the pot with tongs. Stir in balsamic vinegar if desired. Taste and season with more kosher salt as needed. Garnish with chopped fresh parsley leaves if desired.