Cut beef into 4-6 large chunks and generously season with salt & pepper. Brown beef in batches in olive oil.
Add beef to the slow cooker and add remaining ingredients.
Cook on low 8-10 hours or on high 4-6 hours or until fork tender.
Remove bay leaves and discard. Shred beef with forks and add back to the juices in the slow cooker, cover and cook on high at least 30 minutes.
Serve with tortillas.
