50 g butter
1 onion, finely chopped
250 g button mushrooms, thickly sliced
500 g lean steak, cut into thin strips
200 g crème fraîche
300 g tagliatelle
Chopped parsley to serve.
Dijon Mustard (optional)

Melt 25g butter in a large frying pan and cook the onion until soft.
Add the mushrooms and cook over a high heat until golden. Remove from the pan and reserve.
Melt 25g butter over a high heat and cook the steak, in batches, stirring, for about 3-4 minutes until well browned. Be sure the fat in the pan is hot again before adding the next batch.
When all the meat is cooked, return it to the pan, add the onion, mushrooms, mustard and crème fraiche and warm gently.
Serve the beef on top of the cooked tagliatelle and top with chopped parsley.