• Put the butter and oil in a large soup pot, over medium heat, then add the leeks and onion. Saute for about 5 to 6 minutes, stirring often. You can cover the pot in between stirring.
• Add the chicken broth to the leeks and onion and bring to a simmer.
• Next, add the chopped potatoes and continue to simmer, stirring occastionally until potatoes are soft. Add some salt to taste.
• Once the potatoes are cooked, remove from heat and blend with an immersion blender, or place in a traditional blender to puree until smooth.

At this point, the soup is ready to eat, however, unless you or someone in your family is lactose intolerant, I would advise adding one of the following, more or less, to your liking: milk (or half and half/heavy cream). It makes the soup more creamy and delicious. After adding the milk and/or cream, taste for salt, and add pepper if desired. You can also just add a little milk and or cream into individual bowls for individual preferences, too.