Trim off and discard the dark green portion of the leeks, as well as the roots.
Slice the leeks lengthwise and swish around in a bowl of cold water to wash out the sand and dirt (leeks are very sandy), then drain.
Slice across the leeks to produce small half-moon shapes about ½″ wide.
Add butter to pot and melt.
Add leeks to pot, and a big pinch of salt (maybe ½ t) and sweat on medium until soft.
Add potatoes and vegetable broth. Raise heat to barely bring to a boil, then reduce heat to medium low and simmer until potatoes are soft (30 – 45 minutes).
Turn off heat and puree in blender (in batches if necessary) or use an immersion blender if you have one, then return to pot.
Optional – If you like chunks of potatoes, add the extra ½ Lb now, return to heat and simmer until soft.
Add cream and buttermilk, and salt and pepper to taste.
Serve in bowls with a sprinkling of chives over the top.
