Sauerkraut-bulgur soup

1 sm Onion, chopped
    1/4 c  butter
  2 3/4 c  Sauerkraut
    1/4 c  Tomato puree
      1 lg Russet potato, diced
    1/2 c  Bulgur, fine grade
      2 qt Rich chicken or veal stock
           Salt
           Pepper
           Sliced green pepper
           parsley
 
  Armenian culture is rich in soups, many of them made tart with yogurt
  and thickened with bulgur. This version is flavored with sauerkraut.
  From "Armianskala Kulinaria," by A.S. Piruzian.
  
  In 5-quart pot, saute onion in butter until golden. In bowl, soak
  sauerkraut in water, drain and chop. Add to onions and cook until
  done, adding water if mixture gets too dry. Add tomato puree. Saute
  5-7 minutes.
  
  Add potatoes, bulgur and stock and cook 15 minutes. Season to taste
  with salt and pepper. Garnish with slight green pepper and parsley.