1 tb Unsalted margarine 1 md Yellow chopped onion 1 md Chopped leek 1 md Chopped stalk celery 2 md All purpose potatoes (about 1/2 lb) peeled and Diced 1 3/4 c Low salt chicken broth 1 c Buttermilk 1 tb Minced fresh/freeze Dried chives 2 ts Lemon juice 1/4 ts Hot red pepper sauce In a large heavy saucepan melt the margarine over moderate heat. Add the onion, leek and celery and cook, uncovered, stirring, occasionally, until the vegetables are tender, 6-8 minutes> Do not brown. Add the potatoes, stir in the chicken broth and bring to a boil. Reduce to simmer and cook until the potatoes are tender, about 20 minutes. In blender or food processor, puree the soup in 2 or 3 batches, whirling each batch about 30 seconds. Stir in the buttermilk, chives, lemon juice and red pepper sauce. Cover the soup and refrigerate at least 2 hours before serving. Thin with additional cold buttermilk if desired.