This cold, potato soup only needs 2-3 potatoes and is pretty easy to make. It does need to be chilled for at least 8 hours, so I usually make it the day before and let it chill overnight.
Sauté onion and butter in stock pot over medium heat until golden, about 5-6 minutes. Stir often so the onion doesn't burn. Add potatoes, broth and salt. Cover and cook until potatoes are tender, about 10-15 minutes. Cool until lukewarm.
Pour half of the potatoes and broth into a blender or food processor. Cover and process until smooth. Repeat with rest of potatoes and broth.
Pour into bowl and add light cream, stirring to mix well. Chill for several hours or overnight. Just before serving stir in heavy cream. Garnish with chopped chives.