A friend and I were recently chatting about cold soups. Most people immediately think of gaspacho, which I've never really cared for. There are very few soups meant to be enjoyed cold, but vichyssois (vee-she-swah) is in my mind the absolute king. A little bit of history here, but if you aren't interested in that, feel free to skip to the recipe below.
Despite what you would think, vichyssois is not, in fact French, but rather an American dish from about a hundred years ago. Back then, more or less any time you invented a new recipe, you would give it a French namesake (whether to honor where you were trained, the tradition you were trained in, to make it sound fancier and let you charge more...well, that's up to you.) if you didn't name it after where the recipe was invented (i.e. the Waldorf salad).
Now, it would be a bit much to claim that we in the US invented potato leek soup, which vichyssois is a varient of, but it is very, very different in character.
In the 1980's, there was a big case of a couple who died of botulism from consuming canned vichyssois. Botulism toxin is one of the absolute deadliest toxins on earth- it would take about ten grams to kill every human being on the face of the earth. Funny thing is, it's destroyed by heat. So even today, people who hear about the death of this couple are mystified as to why they died. It's a canned soup, the only way it would have killed them were if they just ate it straight from the can.
Well, that's exactly what they did. Why? Because vichyssois is meant to be served cold, a fact which was explained on the label, that it could be enjoyed cold straight from the can.
Now, I personally am repulsed at the idea of consuming a cold canned soup, but that's because canned soups are generally meant to be served hot and are slimy if they are consumed cold. For all I know, this vichyssois wasn't, but I really don't want to find out.
This does however prompt me to hammer home that vichyssois is as safe as anything else you cook in the kitchen. There aren't any inherent toxins to be destroyed, this was simply a case where the canning process failed and the food was contaminated from outside. So your home made vichyssois should be fine.
Peel 6-8 large russet potatoes, and cut into quarters (or cut so that the pieces are roughly equal in size). Clean and chop roughly half that amount of leeks (make sure to slice lengthwise and clean out any dirt present). You absolutely can eat most of the green part of the leeks. Dump into a large pot and add water until the vegetables are just covered. Cover the pot and heat on a high heat until the potatoes are tender.
Now, this is a great opportunity to use that stick blender gathering dust in the back of your kitchen. Don't drain the vegetables, but instead blend the contents of the pot with the stick blender. If you do not have a stick blender, you can absolutely do this with a regular blender, but it will be a bigger pain in the butt.
Once the contents are blended, toss a cut up stick of butter in and stir until it has melted.
Add salt and pepper to taste, then refrigerate the pot until cold (likely overnight).
Once the soup is cold, add cream and stir. The color should be a pale green, which doesn't take all that much cream. Again, check your salt and pepper, and serve with a nice piece of buttered, freshly baked bread. This may be enjoyed for any meal of the day.
A word of caution
Add the cream after the soup has chilled. Adding the cream and then chilling can promote bacterial growth.
I like to transfer the chilled soup into a pitcher to make it easier to dispense, and to take up less space in my fridge, but YMMV.
This is a particularly great use for older potatoes, because the starches in the potato have begun to break down into sugars, producing a slightly sweeter and more flavorful soup.