A winter warmer....
1. Put the oil in a large saucepan with a tablespoon of water. Add the leeks, stir and cover with a lid. Cook over a very low heat, stirring occasionally for 10 minutes. Do not let the leeks brown or burn.
2. Add the celeriac and potatoes and the stock. Bring to the boil and turn down to a simmer. Cook, covered, for approximately 25 minutes or until the celeriac and potatoes are tender.
3. Puree the soup in a blender and put back in the pan. Add the milk to make a good consistency and season with freshly ground black pepper. Reheat to just below boiling point to serve.