Beef Stroganov

Peel and cut the onion into very thin slices and clean and cut the mushroom caps into thin slices. Cut the beef into little finger size pieces  Picture  .

Put a pan over a high heat, season the beef with salt and black pepper and cook very quickly on both sides for a couple of minutes. Take out of the pan and keep to one side. Put a little more butter in the pan, add the onions and cook over a medium heat, turning from time to time, for about five minutes.

Meanwhile put the water on for the pasta and add the tagliatelli when boiling. Cook for about five minutes or whatever the carton says.