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 stock with tomato paste and Worcestershire sauce in a jug until smooth. Pour over beef. Stir to combine. Cover and cook on high for 1 and 1/2 hours or until wallaby is tender. Stir in sour cream and season.