3. In a large pan, over medium heat melt butter. Add steak in a single layer and cook for 2-3 minutes per side, until browned. (Work in batches, if your pan isn't big enough). Remove cooked steak from the pan and transfer to a plate
5. Add wine and stir to deglaze the pan. Add stock, Worcestershire sauce and flour. Stir to combine. Cook for about 5 more minutes, stirring frequently until the sauce thickens. Add sour cream (or heavy cream). Cook for just 1 minute, to warm up.