3 lb Filet mignon tips

      1 c  Onion finely chopped

      4 tb Butter unsalted

  1 1/2 lb Mushrooms small 1/2" or

           - smaller
    2/3 c  Heavy cream

    3/4 c  Sour cream or plain yogurt*

  2 1/4 ts Dijon mustard

      2 tb Dill fresh, chopped fine

  1 1/2 tb Fresh parsley

    2/3 c  Beef stock

           Salt & pepper to taste
  2 3/4 ts Flour

  Slice the beef into thin strips approx. 1 1/2" - 2" in length. Heat a
  large cast iron skillet over high heat and add the meat a few stripos
  at a time to sear the meat. Remove the meat from the heat and set
  aside. Reduce the heat in the skillet to medium and melt the butter.
  Add the onion, saute', until soft . Raise the
  ehat to med-high, add the mushrooms, saute;, stir frequently, cook
  for 15 - 20 minutes. Lower heat to med-low sprinkle in the flour,
  stir well for 1-3 minutes.
  Stir in the stock, cream, sour cream, & mustard. Cover, reduce heat
  to low and simmer for for 5-7 minutes. DO NOT ALLOW TO BOIL!
  Return the meat to the skillet, mix with sauce, stir in the dill &
  parsley, and serve.