Season and brown the beef. Allow about 20 minutes for chopping the vegetables and browning the beef. Pat the beef dry, season it with the salt and pepper, and toss it with the flour. Heat the olive oil in a large skillet over medium-high heat and brown the beef in two batches, 8 to 10 minutes total, until browned on all sides.
Layer the vegetables. Put the potatoes, carrots, celery, onion, and garlic in the bottom of a 6-quart slow cooker.
Add the beef and broth. Set the browned beef on top of the vegetables. Stir the beef broth, tomato paste, Worcestershire sauce, and thyme together and pour the mixture over the beef. Tuck the bay leaves into the pot.
Cook low and slow. Cover and cook on LOW for 8 hours, until the beef is fork-tender and the potatoes are soft when pierced with a knife. Do not lift the lid during cooking.
Finish and serve. Remove and discard the bay leaves. Check the stew with a food thermometer — it should reach 165°F. Taste and add salt if needed, then ladle into bowls and serve hot.