Crockpot Creamy Meat Balls

1/4 Cup butter
1Medium onion, chopped
2 Pounds ground beef
2 Eggs
2 Teaspoons salt
1/2 Teaspoon pepper
1/4 Teaspoon tarragon
1/4 Teaspoon marjoram
2 1/2 Tablespoons flour
5 1/2 Tablespoons tomato paste
3/4 Cup beef stock
4 Teaspoons Worcestershire sauce
2 Teaspoons vinegar
1/2 Pound mushrooms, sliced
1 Cup sour cream

Saut� onion in half the butter in large fry pan until golden brown. Put the onion in the crockpot. Mix together the beef, eggs, salt and pepper. Form into small balls. 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 saut� mushrooms for minutes. Add the mushrooms and the sour cream to the meatballs and heat through.