Heat the oil in a wide and add the beef in batches. Sear over a high heat then transfer to the slow cooker.

Add the onion, garlic and paprika to the pan and cook for a few mins until soft, Add a splash of water and scrape any bits from the bottom of the pan. Place everything into the slow cooker.

Add the stock to the beef, then the mustard. Add enough water to just cover the beef, put the lid on and cook on Low for 6-8 hrs or High for 5-6 hrs.

About 20 mins before serving, melt the butter in a frying pan and cook the mushrooms until soft and caramelised. Tip into the slow cooker. Mix the cornflour with a little liquid from the stroganoff in the frying pan until smooth, then add about 100ml more and bring to a simmer.

Once thickened, pour into the slow cooker with the sour cream. Turn to High (if not already) and cook for another 20 mins.

Serve with tagliatelle sprinkled with paprika.