Don't let the stories of gritty leeks scare you. They are actually pretty easy to wash and they add a wonderfully mild onion flavor. Potato leek soup comes in many varieties and can be served hot or cold.
To prepare the leeks: Cut the hard root end and the dark green tops off the leeks. Cut the remaining white and light green part in half, lengthwise. Slice thinly.
Fill a big bowl or stock pot with tap water. Add the sliced leeks. Use your hands to separate the layers of leek and the swirl the leeks in the water. Let sit for a couple minutes for the leeks to float to the top and the dirt to sink to the bottom. Using your hands, or a slotted server, scoop the leeks gently from the water without stirring so you do not disturb the dirt. Voila! Clean leeks.
In a soup pot, heat olive oil or butter over medium heat. Add the leeks and sweat until translucent. (Optionally, add sliced garlic at this point but be careful not to burn the garlic.)
Add the diced potatoes and stir to coat.
Add the broth and simmer for 20 minutes or until the potatoes are soft. The larger the pieces of potato, the longer this will take. Test a piece of potato to make sure it has lost its "raw" taste.
At this point you have many options for finishing the soup. You can choose whether to add milk or cream, whether to blend or thicken the soup, how to season or garnish the soup, etc. Some suggestions follow:
Option 1: Season with salt and pepper and process in a blender or with an immersion blender until smooth. Serve hot or cold.
Option 2: Thicken with a roux made by sauteing together flour and butter in equal portions (e.g. 2 tablespoons each) in a separate pan. Spoon some soup into the roux and stir until smooth and somewhat liquid. Add this mixture to the large pot of soup and simmer until the soup has thickened. Season with salt and pepper. Taste to make sure the flour has lost its "raw" taste before removing from the heat. Serve hot.
Option 4:When potatoes are tender break up potatoes with a masher, add a can of evaporated milk and heat just under boiling. Season with salt and pepper. Serve hot.
Other options: Add garlic, parsley, celery or other ingredient to add flavor. Use seasoned salt, lemon pepper, or other spice mixture. Garnish with crumbled bacon, snipped chives, green onions, croutons, grated cheddar, or a dollop of sour cream. Use your imagination.