Onion Soup

I love soups. They're probably my favorite food - warm and comforting, and still a fairly light meal. I was prejudiced against onion soup for years, but an acquaintance who is a chef finally convinced me to try it (and gave me this recipe). I find it incredible how something with so few ingredients (the main one of which is the humble onion) can be so amazingly rich and tasty.
This soup is served with cheese. I usually use gouda or edam (as for everything else, really), but any cheese that melts and doesn't have a very strong taste will do.
I haven't yet tried the famous French onion soup, which is usually done with a sharper cheese, but it's on my "to make" list, so I'll let you know when I do.

Ingredients:

1 kg/2 lb 3 oz onion
2 stock cubes
1 cup sour cream
water
1 tsp sugar
cheese
toast
salt, pepper
oil
water

Peel the onions and chop or slice them roughly. Heat oil in a casserole and add the onions. Cook for about 30 minutes - without water at first, stirring often. If the onion start changing color, add a bit of water. When the onion is softened and transparent puree it in a blender or food processor (a hand blender will do as well). Return to the casserole, add the stock cubes (you could use real stock if you have some, but the cubes work just as well), 1 tsp of sugar and 1.5 l of water. Mix the sour cream with a bit of water and stir it in as well. When the soup starts boiling try it and add salt and pepper to taste.
Pour in bowls, grate or slice cheese on top and serve with toast or croutons.