Wash leeks very carefully to remove any dirt. I usually cut them horizontally and separate the rings to make sure no dirt remains. Coarsely chop them when washed.

In a medium soup pot, melt butter and add flour on low heat. Using a wooden spoon, mix well. This will thicken your soup and give it a wonderful flavor.

Add chicken stock, leeks, onion, potatoes and bring to a boil. Cover and simmer on low for about 20-25 minutes, until potatoes are soft.

Using an immersion blender, blend the soup until smooth adding the milk and adjusting salt and pepper to taste. Serve immediately