Slice the beef into thin strips, approximately 1.5 to 2 inches in length.

Heat a large cast iron skillet over high heat.

Add the beef strips a few at a time to sear the meat quickly and evenly.

Remove the seared meat from the skillet and set aside.

Reduce the heat in the skillet to medium and melt the unsalted butter.

Add the finely chopped onions and sauté until translucent.

Add the sliced mushrooms and cook until softened.

Lower the heat to medium-low and sprinkle in the all-purpose flour, stirring well for 1 to 3 minutes to create a roux.

Stir in the beef stock, heavy whipping cream, sour cream, and Dijon mustard until well combined.

Cover the skillet, reduce the heat to low, and simmer for 5 to 7 minutes, stirring occasionally.

Do not allow the sauce to boil.

Return the seared beef to the skillet and mix it with the creamy sauce.

Stir in the fresh chopped dill weed and parsley leaves.

Serve the Ukrainian Beef Stroganoff hot over egg noodles, rice, or mashed potatoes.