Place the potatoes and leeks in a large saucepan then add just enough water to cover. Over a high heat, bring the water to the boil and sprinkle in the stock cubes. Lower to a simmer and cook for about 10 to 12 minutes or until tender.
Once tender, using a handheld liquidiser, blend the ingredients together to form a soup, adding a little extra stock or some milk to bring it to the desired consistency. Add the salt to taste then stir through the cheese to serve.