It’s tasty, good for your health, but not so good for your breath:) But a good old mint always solves the problem.
Place a medium soup pot over medium heat. Add the butter, olive oil, and diced onion. Cook, stirring occasionally, until the onion is softened, about 3 minutes. Add the leak, diced potato, diced garlic and cook continue cooking for 5 minutes. Add the stock and salt, and bring the mixture to a simmer. Simmer for about 10 minutes and then our the soup into a large bowl. Carefully ladle 1/2 of the soup into a blender and puree until smooth. Be careful to hold the top of the blender very tightly, because hot liquids expand when they are blended. Pour the blended soup back into the soup pot. Now blend the remaining soup. Once all the soup is blended, add milk and pepper. If you have a “stick” hand blender, you can save the trouble and blend the soup directly in the pot.
Serve hot, with bread rings or croutons.