Four leeks, tough greens removed, thinly sliced Three tablespoons butter Two large or three medium Yukon Gold potatoes, peeled and diced One quart chicken broth One cup half and half One cup heavy cream Salt and white pepper to taste Chopped chives for garnish (optional)      First and foremost:  leeks are a very gritty onion and must be cleaned thoroughly.  Cut off the root end and then cut the green end where the greens start to get tough.  Slice the leek lengthwise and open up the layers under running water.  Then slice them thinly crosswise.  Lightly sweat the leeks in the butter.  Add the potatoes and chicken broth.  Bring to a boil and then immediately reduce to a simmer until the vegetables are completely soft, 20 & 25 minutes.  Add the half and half and the cream and bring back to a simmer.  Strain the soup through a fine mesh sieve, crushing and pushing the potatoes through it.  Some folks put it in a blender before straining it.  If you do, puree it briefly.  Overworking the starch in the potatoes can make the soup gluey.  Add salt and pepper to taste.  Chill the soup with plastic wrap resting right on top of it to prevent a film from forming on the surface.  Ladle it into chilled bowls and sprinkle with fresh chopped chives if you like.   If you're watching your calories and/or fat content you should avoid this soup altogether.  Eliminate the half and half and cream and simply make a hot potato-leek soup.  It is still delicious.  If you wish to be semi-decadent, keep the cream and substitute water or vegetable broth for the chicken broth.  Or reduce the half and half and cream and use more broth.  However, the soup will not be as rich and smooth.  Your choice.