|Butter||5 Ounce (50 Gram)|
|Vegetable oil||2 Tablespoon|
|Onion||1 Large, chopped|
|Leeks||3 Medium, thinly sliced (White Part Only)|
|Potatoes||6 Medium, finely chopped|
|Chicken stock||1 1⁄2 Pint (900 Milliliter)|
|Milk||10 Ounce (300 Milliliter)|
Melt the butter with the oil in a large saucepan.
Add the onion and fry until it is soft.
Stir in the leeks and potatoes and cook, turning occasionally, until the potatoes are evenly browned.
Season with salt and pepper and pour over the stock and milk.
Bring to the boil, stirring constantly.
Reduce the heat to low, cover the pan and simmer for 20 to 25 minutes, or until the potatoes are very tender.
Pour the soup through a strainer into a bowl, using the back of a wooden spoon to rub the vegetables through.
Discard the pulp in the strainer.
Alternatively, puree the soup in a blender.
Return the soup to the saucepan and simmer for 5 minutes.