Adapted from "The Beekman 1802 Heirloom Vegetable Cookbook". Tangy buttermilk and rich nuts tame the peppery flavor of raw red radishes, which give this refreshing soup a purple-pink hue (although you can use radishes of other colors). Although the soup makes a lovely first course for a casual dinner, you could also set out smaller servings in shot glasses for an elegant outdoor-party appetizer. Make Ahead: The soup can be refrigerated for up to 1 week or frozen for up to 3 months. The garnishes can be refrigerated for up to 3 days; the sliced radishes should be stored in water to prevent discoloration. This can be made vegetarian by omitting the egg garnish, and vegan by substituting the buttermilk for non-dairy milk with vinegar (1 cup non-dairy milk to 1 tbsp. vinegar or lemon juice, let stand 5 minutes to curdle). "Cook" time is chilling time.