At Cass's request. This is so simple, but so tasty. It's adapted from Mark Bittman's How to Cook Everything.
some potatoes (I used five smallish russets)
some leeks, an equal number to the potatoes (I actually only had three, but they were large)
veggie or chicken stock
salt and pepper
sour cream (I used Cabot's Light; you could also use plain yogurt or milk/cream)
Peel and dice potatoes. Thinly slice white and light green parts of leeks. Sauté potatoes and leeks in a medium-large stockpot in a bit of olive oil or butter for a couple of minutes, just to wilt the leeks—do not let veggies brown. Generously salt and pepper, then add stock to about an inch above level of veggies. Bring to a boil, then cover and simmer until veggies are very tender, about 20 min.
Off heat, use immersion blender or food processor to purée soup. Add sour cream (or yogurt or milk) to taste (I used about 3/4 c.) and blend until well mixed.
Garnish with fresh parsley or dill or whatever else strikes your fancy and you have in your fridge. If you're me, eat with a reheated piece of naan from your work send-off lunch.