I think this is a common recipe (although my proportions may be a little different) however it is very nice.1 oz butter
2 medium onions
3 leeks
2 medium potatoes
2 pints Chicken stock
Salt and Pepper
Chop the onions leeks and potatoes into small pieces
Melt butter in a saucepan, sweat the onions and leeks (Do this gently, brown bits are not good) once they are soft add the chicken stock, salt, pepper, and the potatoes.
Cover and cook until the potatoes are soft.
Liquidise. I eat (drink?) this warm, however it is good served from the fridge as well. I have seen recipes which add a swirl of cream, but I haven't tried this myself.
If you like it thicker add more potato, if you like it thinner add more chicken stock.