Preheat oven to 400°F (200°C).

Chop leeks and potatoes into large pieces.

Sauté the chopped leeks in a pot over medium heat until they are softened and lightly browned, about 10-12 minutes.

Add the chopped potatoes, chicken or vegetable broth, and milk to the pot.

Bring the mixture to a boil, then reduce the heat to low and simmer for 20-25 minutes, or until the potatoes are tender.

Purée the soup using an immersion blender or a regular blender until smooth.

Season the soup with salt and pepper to taste.

Serve the soup hot, garnished with chopped fresh herbs if desired.