Cuban Ropa Vieja

Heat vegetable oil in a large frying pan over medium-high heat. Brown the flank steak on each side, about 4 minutes per side.

Transfer beef to a slow cooker. Pour in the beef stock and passata, then add the onion, green pepper, garlic, tomato puree, cumin, coriander, olive oil and vinegar. Stir until well blended. Cover, and cook on High for 4 hours, or on Low for up to 10 hours. When ready to serve, shred meat and serve with tortillas or rice.