01 - Season beef cubes with salt and freshly ground black pepper.
02 - Heat olive oil in a large skillet over medium-high heat and brown beef cubes in batches, about 3 to 4 minutes per batch. Transfer browned beef to the slow cooker.
03 - Add carrots, potatoes, celery, onion, and garlic to the slow cooker with the beef.
04 - Whisk beef broth, tomato paste, Worcestershire sauce, and red wine (if using) in a bowl, then pour over beef and vegetables.
05 - Add dried thyme, rosemary, and bay leaves; stir gently to combine.
06 - Cover and cook on low for 8 hours or on high for 4 to 5 hours, until beef and vegetables are tender.
07 - Thirty minutes before serving, stir cornstarch or gluten-free flour into water to form a slurry. Add to the slow cooker along with frozen peas and cook uncovered for 30 minutes until thickened.
08 - Remove bay leaves, taste, and adjust seasoning as needed before serving.