1Start with some nice beef fillet, trim it up and get it sliced and into a hot pan.
2You want really really good color on this. We're not trying to cook anything rare or medium. We can cook this well and get really nice fond on the bottom of the pan.
3Add chopped onions to the pan.
4Add sliced mushrooms and cook until they start releasing their liquor.
5Add a little bit of flour to the pan.
6Add Worcestershire sauce and a little bit of mustard.
7Add rich beef stock.
8Add sour cream to make a thick kind of gravy.
9Add the seared beef to the pan.
10Cook the sauce for about 30-35 minutes.
11Finish with some flat leaf parsley and some lemon juice.
12Serve over hot buttered tagliatelle egg noodles.