Place the flour in a shallow dish and season with salt and black pepper.
Dredge the beef cubes in the seasoned flour, shaking off any excess.
Heat the vegetable oil in a large skillet over medium-high heat.
Add the beef cubes in batches and brown on all sides, about 4-5 minutes per batch. Transfer browned beef to the slow cooker.
In the same skillet, add the chopped onion and cook for 3-4 minutes until softened.
Add the minced garlic and cook for 1 minute until fragrant.
Transfer the onion and garlic to the slow cooker.
Add the carrots, parsnips, celery, and pearl onions to the slow cooker.
Pour the brown ale and beef broth over the ingredients in the slow cooker.
Stir in the tomato paste, Worcestershire sauce, fresh thyme leaves, and bay leaves.
Season with additional salt and black pepper to taste.
Cover and cook on low heat for 8 hours, or until the beef is tender and the vegetables are cooked through.
Remove the bay leaves before serving.
Garnish with chopped fresh parsley and serve hot.