Leek,Potato and Onion Soup

A great believer in soups, here's another one....
LEEK, ONION AND POTATO SOUP
For 4 – 6 people you will need..
4 large leeks
2 medium potatoes, peeled and diced
1 medium onion, chopped
50g butter
850 ml chicken stock /water
275 ml milk
Salt and pepper
To serve :1 ½ tablespoons chopped chives ( I buy frozen herbs in winter….available in all supermarkets here)
2 tablespoons crème fraîche (optional)

Trim off the tops and roots of the leeks, discarding the tough outer layer. Slice them up finely and rinse thoroughly.In a large pot, melt the butter and add the leeks, potatoes and onion stirring them with a wooden spoon. Season with salt and pepper, cover and let the vegetables sweat over a very low heat for about 15 mins.Then add the stock and milk, bring to a simmerinig point, replace the lid and simmer very gently for 20 mins. Liquidise to a purée. Reheat very gently. Add the chives and the cream just before serving.