From The Heart of the Plate by Mollie Katzen
Simple and tasty - I had mushrooms and scallions that I wanted to use up, so I added those too.
INGREDIENTS:
1 lb russet potatoes, peeling optional, into 1 inch chunks
4 cups water
up to 1.25 tsp salt
2 Tbsp olive oil
4 packed cups (~2 lbs) cleaned leek rings, short of 1/4" thick
(plus ~ 1/2 - 1 cup sliced mushrooms, and one large scallion)
Black pepper
DIRECTIONS:
1. Combine the potato chunks, water and 1/2 tsp salt in a medium-large saucepan. Bring to a boil, then lower the heat to a simmer and cook, covered, until the potatoes are very soft, about 15-20 minutes.
2. Meanwhile, place another saucepan over medium-low heat for 1 minute. Add the OO and swirl, then add the leeks and another 1.2 tsp salt and cook. Stir for a minute or two, then lower the heat and continue to cook, stirring for 5-8 minutes. Cover and cook over low heat for another 5-8 minutes, or until the leeks are very soft.
3. Add the potatoes and all their cooking water to the leeks, along with black pepper to taste. Cover the pot, turn off the heat, and let the soup sit for about 15 minutes to develop the flavor. Somewhere in there, taste to adjust the salt.
4. You can now reheat the soup and serve as is or puree some of it with an immersion blender and reheat. Serve hot. Note - I didn't care for the way it looked, so I blended all of it, in batches, in my Bullet, then seasoned with salt and pepper.