Combine flour and salt; dredge beef strips in the mixture.

Heat skillet with 2 tablespoons of butter.

Brown beef strips quickly on all sides in the skillet.

Add mushroom slices, onion, and minced garlic to the skillet.

Cook until onion is tender (3-4 minutes).

Remove beef and mushrooms from the skillet and set aside.

Add 2 tablespoons of butter to the pan drippings.

Blend in 3 tablespoons of flour and add the tomato paste.

Slowly pour in the cold beef stock, stirring constantly.

Cook until the mixture thickens, ensuring no lumps form.

Return browned beef and mushrooms to the skillet.

Stir in sour cream and cooking sherry.

Heat briefly, do not boil.

Serve hot over noodles or rice.