I didn't have leeks, but had sweet Vidallia onions. The soup was obviously not the same as a true Vichyssoise, but nice on a hot evening anyway. I'm going to skip the photography because we all know what potato soup looks like and there's no way to make it look fancy, save for some chopped chives. I based this on the Julia Child recipe in Mastering the Art of French Cooking, though she would undoubtedly disapprove of using vegetable stock and sweet onions.
You Will Need:
3 cups peeled and sliced potatoes
3 cups sliced sweet onions (or leeks if you have them)
1 1/2 quarts vegetable stock
Salt to taste
Pepper to taste (and no, you don't have to use white pepper)
1/2-1 cup heavy whipping cream (yeah, this isn't health food, but it is served in tiny cups so it isn't like you're going to eat the whole tureen at one sitting). I used 1/2 cup and it was fine.
In a large pot, simmer the potatoes and onions in the stock with the lid slightly vented for about 40 minutes, or until vegetables are soft. Puree in a food mill, then through a fine sieve. You can use a blender if you have one-I do not. Stir in the cream, and adjust the salt and pepper. Serve well chilled in chilled bowls (five minutes in the freezer should do it).
Adorn with chopped fresh chives if you must.