Put the beef, onion, mushrooms and garlic into the slow cooker.
Mix the stock cube with the 250ml boiling water, then add the Worcestershire sauce, Dijon mustard, tomato purée, smoked paprika and black pepper.
Whisk in the flour, then pour the whole mixture over the beef.
Cook on HIGH for 4 hours.
When the beef is tender, stir in more sliced mushrooms and the 150ml sour cream.
Add a splash of double cream if you want it extra creamy, then finish with chopped parsley.
