My version of Vichyssoise is thicker than traditional Vichyssoise, because when that's all I'm having for lunch I want it to really fill my belly. If you want it thinner, like you might for a first course at dinner, you can always add more water or cream just before serving.
Vichyssoise (makes about 3 ½ quarts)
700 g russet potatoes (about 5 large potatoes)
700 g leeks (about 6 thick leeks, white and pale green parts only)
140 g unsalted butter (about 1 ¼ sticks)
1 pint organic heavy cream
3 quarts water
fresh ground black pepper
Remove the dark green parts of the leeks and discard (or save for later use in a vegetable stock). Cut the white and pale green part of the leeks into quarter circles of the same size and rinse them completely under cold water. Leeks have tons of dirt in them usually, so you really want to wash them well. The best way I've found is to use a salad spinner, completely submerge them in water, swish them around a lot, then dump the water. Submerge them a second time, swishing again, and dumping the water. Depending on how much dirt you see (or how clear the water is when you dump it the second time) you may want to give them a third rinse. Then spin/strain them to get out most of the water.
Peel the potatoes and rinse them under cold water. After rinsing them, cut them into pieces roughly as thick as the leek quarters. Don't rinse them a second time, unlike with mashed potatoes, with soups you want to retain a fair amount of the starch in the potatoes and rinsing them a second time removes too much starch.
In a heavy stock pot, melt the butter, then add the leeks and a pinch of salt and sauté to sweat and soften them a little, stirring for about 3-5 minutes on med-high heat. Don't let them take any color. When they've softened, add the potatoes and mix well, then add the water. Bring to a boil, then reduce heat to a simmer and cook, uncovered, for about 35-45 minutes until the potatoes are falling apart and the leeks are completely soft and cooked.
With a hand blender or in a stand blender in several batches, purée the soup very well, leaving no chunks at all. Add the cream and whisk to incorporate. At this point, you want to taste it to see if you'd like to add more salt. I always do add some more, but everyone's taste varies with salt, just add it cautiously because you can't take salt away from something that's too salty.
Pour the Vichyssoise into containers, allow it to come to room temperature, then cover and refrigerate until completely chilled. When the Vichyssoise is completely cold, it will thicken up, then you can try some and see if you'd prefer to have it thinner by adding more water or cream. I usually make it thinner if I'm serving it as an appetizer, but I do that à la minute and leave it thick in my fridge for lunches. Vichyssoise keeps in the fridge for about a week (just make sure the date on the cream you use is good for at least that long too).
Serve the Vichyssoise (hot or cold) garnished with chopped chives and freshly ground black pepper.