Add the beef cubes, quartered mushrooms, diced onion, and sliced celery to the slow cooker.
In a small bowl, whisk together the beef bone broth, tomato paste, minced garlic, dried thyme, dried rosemary, salt, and black pepper until smooth.
Pour the broth mixture over the meat and vegetables in the slow cooker, then add the bay leaves.
Stir gently to combine everything, cover, and cook on low for 8 hours.
Remove the bay leaves, stir the stew once more, and serve hot.