Dry-brine the roast. Pat the chuck roast dry and season all over with 1 tablespoon kosher salt. Place it on a rack and refrigerate uncovered overnight (or at least 12 hours). → Let it sit at room temp for 30 minutes before cooking.
Sear the roast. Preheat oven to 300°F. Heat oil in a Dutch oven over medium-high. Sear roast on both sides until deeply browned. Remove and set aside.
Sauté aromatics. Lower heat. Add chopped onion and cook at least 5 minutes, scraping up brown bits. Add celery, garlic, thyme, rosemary, bay leaves, and dry seasonings. Cook 5 more minutes, keeping the garlic cut side down. Add wine and simmer 2–3 minutes.
Braise the roast. Return roast to the pot and nestle into aromatics. Pour in 2 cups broth (don’t fully submerge). Bring to a simmer, cover tightly, and transfer to oven. Cook for 3 hours.
Strain and thicken. Remove roast and strain out aromatics. Press them through a fine-mesh strainer to extract flavor. Add the reserved ½ cup broth mixed with 2 tablespoon cornstarch and stir well.
Add veggies. Add carrots, potatoes, and sliced onion to the pot. Nestle roast on top. Bring back to a simmer, cover again, and return to oven for 1 more hour.
Shred and serve. Remove pot from oven and uncover. Use two forks to shred the roast directly in the gravy. Serve with crusty bread or cornbread for soaking up every drop.