Slice the leeks (I used three for the above amount of potatoes) finely and cook in a lidded pan with a generous amount of butter until silky soft. Meanwhile, chop the potatoes into small pieces and boil for about 5min, in the microwave is fine. Drain, then roughly break up with a fork, before adding to the softened leeks. Add half a litre of stock and simmer for a few minutes, adding salt and pepper to taste. Serve with a swirl of cream and perhaps some grated Parmesan if you want to remove the peasant feel. The above measurements are rough I know, but I got two big bowlfuls from it. You could easily increase the quantities and freeze leftovers for a later date.
Very easy, very tasty, possibly a bit unseasonal, but the sky was grey and there was a light spattering of rain in my part of London.