Toss & Sear Beef: Pat the cubed halal beef chuck roast dry with paper towels. In a large bowl, toss beef with flour, salt, and black pepper until lightly coated. Heat olive oil in a heavy skillet over medium-high heat. Sear beef in batches for 2-3 minutes per side until deeply browned and caramelized. Transfer seared beef into the slow cooker insert.

Deglaze the Skillet: In the same skillet over medium heat, add the diced onions and cook for 2 minutes. Stir in the minced garlic and tomato paste for 60 seconds until fragrant. Pour in 1 cup of beef broth, scraping up all the deeply caramelized brown fond stuck to the bottom of the pan. Pour the pan juices directly over the beef in the slow cooker.

Assemble Vegetables & Herbs: Add the halved baby potatoes, sliced carrots, and celery to the slow cooker. Pour in the remaining 2 cups of beef broth, Worcestershire sauce, and balsamic vinegar. Tuck the fresh rosemary sprigs, thyme sprigs, and bay leaves into the liquid. Stir gently.

Slow Cook to Tenderness: Cover with the lid and cook on LOW for 7 to 8 hours (or on HIGH for 4 to 5 hours) until the beef chunks are fork-tender and easily pull apart with gentle pressure.

Thicken & Finish: Discard the bay leaves and herb stems. In a small ramekin, whisk cornstarch and cold water until smooth. Pour into the slow cooker along with the frozen peas. Stir gently, cover, and cook on HIGH for 15-20 minutes until the gravy turns rich, glossy, and thick. Garnish with fresh chopped parsley and serve piping hot with crusty sourdough bread!