Sauté onion in half butter until golden brown. Put onions in slow cooker.
Mix together beef, eggs, salt and pepper. Form into small balls
and brown. Sprinkle on tarragon, marjoram and flour. Shake skillet
to turn meat balls and coat them with flour. Put meat balls into
Mix together tomato paste, beef stock, Worcestershire sauce and
vinegar in skillet without cleaning the skillet from browning the
meatballs. Scrape bottom of pan and cook for 2 minutes. Pour over
Cover slow cooker. Cook on LOW for about 1 1/2 hours.
Melt remaining butter. Sauté mushrooms for 5 minutes.