Preheat your oven to 325°F. Pat the 3 lb beef chuck cut into 1.5-inch cubes cubes completely dry with paper towels — this is essential for a good sear. Season generously all over with 2 tsp kosher salt for seasoning the beef and 1 tsp black pepper, then toss with the 3 tbsp all-purpose flour until evenly coated. Shake off any excess.

Heat 2 tbsp of vegetable oil in a large Dutch oven over medium-high heat until shimmering. Working in 2–3 batches (do not crowd the pan), sear the 3 lb beef chuck cut into 1.5-inch cubes cubes for about 2–3 minutes per side until deeply browned on all sides. Transfer each batch to a plate and set aside. Add more 3 tbsp vegetable oil between batches if needed.

Reduce the heat to medium. Add the remaining tablespoon of vegetable oil to the same pot. Add the diced yellow onion and 3 stalks celery and cook, stirring occasionally, for 5–6 minutes until softened and the 1 yellow onion is translucent. Scrape up any browned bits from the bottom of the pot as you stir.

Add the minced garlic and 2 tbsp tomato paste. Stir and cook for 1–2 minutes until the 2 tbsp tomato paste darkens slightly and smells fragrant.

Pour in the 1 can Guinness stout and stir well, scraping up all the browned bits from the bottom of the pot — this is where a huge amount of flavor lives. Let it bubble and reduce for 3–4 minutes.

Add the 2 cups beef broth low-sodium, 1 tbsp Worcestershire sauce, and 1 tsp brown sugar. Stir to combine. Return the seared 3 lb beef chuck cut into 1.5-inch cubes and any resting juices back to the pot. Nestle in the 2 pieces fresh thyme sprigs sprigs, 2 pieces fresh rosemary sprigs sprigs, and 2 pieces bay leaves. The liquid should come about three-quarters up the 3 lb beef chuck cut into 1.5-inch cubes — add a splash more 2 cups beef broth low-sodium if needed.

Bring the stew to a gentle simmer on the stovetop, then cover with a tight-fitting lid and transfer to the preheated oven. Cook for 1 hour and 30 minutes.

Carefully remove the pot from the oven. Add the 3 medium carrots peeled and cut into 1-inch chunks, 1 lb baby potatoes halved, and 1 medium parsnip peeled and cut into 1-inch chunks (if using). Stir gently to submerge the vegetables in the braising liquid. Return the pot to the oven, covered, and cook for another 40–45 minutes until the vegetables are completely tender and the 3 lb beef chuck cut into 1.5-inch cubes falls apart easily when pressed with a spoon.

Remove the pot from the oven. Fish out and discard the 2 pieces fresh thyme sprigs sprigs, 2 pieces fresh rosemary sprigs sprigs, and 2 pieces bay leaves. Taste the stew and adjust seasoning with 2 tsp kosher salt for seasoning the beef and 1 tsp black pepper as needed. If the gravy seems too thin, place the pot back on the stovetop over medium heat and simmer uncovered for 5–10 minutes, stirring occasionally, until it thickens to your liking.

Ladle the stew into deep bowls and garnish with chopped fresh fresh flat-leaf parsley roughly chopped. Serve with crusty bread, Irish soda bread, or creamy mashed potatoes to soak up the gravy.