Heat the olive oil in a skillet over medium heat. Add the beef stew meat and brown it on all sides for about 5 minutes.
Transfer the browned beef to the slow cooker. Add the diced onion, sliced celery, sliced carrots, and minced garlic.
Pour in the beef broth. Stir in the dried thyme, salt, and black pepper.
Cover and cook on low for 7 hours until the beef is tender.
Stir in the ground nutmeg and fresh spinach leaves. Cover and cook for 10 more minutes until the spinach wilts.