Peel, dice and wash the potatoes and place in a suitable saucepan. Peel and dice the onion and add to the potatoes. Add the stock and tomatoes, bring everything to a boil and simmer on a low heat for about 30 minutes, stirring occasionally.
Then puree the soup and season with herbs of your choice and spices.
If the soup is too thin - it`s a matter of taste - it can be thickened with the tomato paste.
As a garnish, I used a dollop of sour cream and a couple of parmesan slices.