Heat skillet and melt 1 tablespoon butter. Add meat and brown quickly, turning meat to brown on all sides.
Add mushrooms, onions, and garlic and cook for 3-4 minutes, until onions are barely tender.
Remove meat and onions and set aside. Add 2 tablespoons butter to skillet. When melted, blend in 3 tablespoons flour. Add tomato paste. Slowly pour in meat stock, stirring constantly until mixture thickens. Return meat and mushrooms to skillet. Add in sour cream and continue to heat briefly.
Serve over rice or noodles.