Using a rolling pin, flatten the steaks to 1cm thick, discarding excess fat and gristle. Cut into finger thickness strips
Drizzle with olive oil, sprinkle with salt & pepper and set aside
Heat 1 tbsp oil in large skillet over a high heat, cook in batches 30 seconds each side of beef strips
Set cooked beef aside
Turn heat down to med-high. Add butter & melt, then add onions & cook for 1 minute
Add mushrooms, cook until golden, scraping all the bits off the bottom of the pan
Add flour, cook 1 minute
Add ½ stock, stirring until incorporated, then add the other half
Stir, add mustard and sour cream, stir some more
Bring to simmer, reduce to low and adjust salt & pepper
Return beef, cook for 1 minute, stir through parsley and serve on pasta
NOTE; Dust the steak with Paprika after the olive oil, S & P
