• Heat the vegetable oil in a skillet over medium-high heat.

• While the oil is heating, dust the beef on all sides with the flour, generously salt and pepper it, then place it in the hot skillet and saute until mostly cooked and brown on all sides, about 3 – 5 minutes.

• When the beef is cooked, lower the heat to medium-low, then remove the beef with a strainer, leaving any juices and oil; put on a plate and set aside.

• Add the butter and onions to the skillet and cook until starting to brown, about 4 minutes.

• Add the mushrooms,  increase heat to medium-high, and stir frequently until the mushrooms are cooked through, gradually increasing the heat as they release their liquid, until all the released liquid has evaporated, about 5 minutes.

• Maintaining the high heat, add the wine, scraping up any brown bits from the bottom of the skillet, and boil until about half of the wine has evaporated, about 4 minutes.

• Stir in the tomato paste, mustard, and beef stock, generously salt and pepper, then continue to boil over high heat until the liquid has reduced by half, about 3 minutes.

• In a small bowl, use a fork and whisk the flour into the sour cream until smooth.

• Use a spoon, and take some of the sauce from the pan and whisk it into the sour cream, bringing it to a lukewarm temperature.

• Reduce the heat to low, return the beef to the skillet, and gently stir in the sour cream, then gradually increasing the heat and bring it to a slow simmer, stirring frequently until the sauce comes together and thickens, about 2 - 3 minutes.

• Remove from heat, and let rest about 10 minutes before serving.  (if serving with pasta, make it while the sauce rests)

• Serve with a wide, flat pasta or over rice or with potatoes.  Delicious.  🙂

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