Season beef. Heat 1 tablespoon of oil in a large frying pan over high heat. Cook beef in 2 batches, for 3 minutes each or until browned. Transfer to a 3L (12 cup) slow cooker.
Heat remaining oil in same pan over medium-high heat. Cook onion and mushrooms, stirring, for 5 minutes. Add garlic and flour and cook, stirring, for 1 minute. Transfer to cooker with paprika. Combine Massel Liquid Stock Beef Style, tomato paste and Worcestershire sauce in a jug until smooth. Pour over beef. Stir to combine. Cover and cook on high for 4 hours or until beef is tender. Stir in sour cream and season.
Serve with mashed potatoes or rice. Sprinkle with chives.