Instructions

  1. Rub both sides of steak with salt and pepper.
  2. Melt 1/2 butter in a large skillet over high heat and brown steak 2 minute per side and transfer to plate.
  3. Reduce heat to medium-high and cook onion, mushrooms and thyme in remaining butter until liquid is released and mushrooms start to brown.
  4. Add flour and cook for 1 minute.
  5. Gradually stir in milk, beef stock and horseradish (or mustard).
  6. Reduce heat and simmer, stirring for 5 minutes until thickened.
  7. Return steak and any accumulated juices to pan.
  8. Simmer steak for 5 minutes or to desired doneness.
  9. Let steak rest for 5 minutes.
  10. Season sauce with more salt and pepper to taste if desired.
  11. Slice steak thinly across the grain and serve with sauce.
  12. Sprinkle with parsley and serve.