Preheat oven to 350°F. In a Dutch oven (5-quart) with a tight-fitting lid, combine beef, tomato paste, vinegar, and flour; season with salt and pepper.
Add onions, potatoes, carrots, garlic, bay leaves, and 3 cups water. Bring to a boil.
Cover, transfer to oven, and cook until meat is fork-tender, 2 to 2 ½ hours.
Remove bay leaves and, if desired, season with salt and pepper before serving.
Place the beef in a 5-quart slow cooker.
Distribute tomato paste, vinegar, and flour over beef; season generously with salt and pepper. Add onions, potatoes, carrots, garlic, and bay leaves.
Cover slow cooker; cook on high until beef is fork-tender, about 5 hours (or cook on low heat 8 hours).
