Brown meatballs in same fry pan. Sprinkle on the tarragon, marjoram and flour. Shake the fry pan to turn the meat balls and coat them with the flour. Put into crockpot.
Mix together tomato paste, beef stock Worcestershire sauce and vinegar in the fry pan, scrape the bottom of the pan and cook for two minutes. Pour over meatballs.
Cover and cook on low for about 1 1/2 hours. Melt remaining butter in and saute mushrooms for minutes. Add the mushrooms and the sour cream to the meatballs and heat through.