Prepare the leeks: Remove roots, outer leaves, and tops. Cut each leek in half lengthwise, then crosswise into 1/2" slices.

Clean the leeks: Immerse the sliced leeks in cold water and swirl to remove any dirt or grit. Drain well.

Boil the broth: Bring the chicken or veggie broth to a boil in a large saucepan over medium-high heat.

Sauté aromatics: Heat olive oil in a large dutch oven over medium-high heat. Add leek, onion, celery, carrot, and garlic.

Cook the vegetables: Partially cover the dutch oven and cook the vegetables for 20 minutes, stirring occasionally, until softened.

Add broth and potatoes: Add the hot broth and cubed potatoes to the dutch oven; bring the mixture to a boil.

Simmer the soup: Cover the dutch oven, reduce the heat, and simmer until the potatoes are tender.

Season the soup: Stir in black pepper and sea salt.

Puree (optional): Serve the soup chunky, or puree it with an immersion blender for a smoother consistency.

Serve hot.