Elderberries grow along many New England roadsides and are a long-time favorite for jelly anti pie. Increase the sugar if this recipe is too tart for your taste.
Combine berries and water in soup kettle. Simmer, partially covered, until berries are soft about 10 minutes. Press mixture through food mill. Return juice to kettle. Combine lemon juice, cornstarch, and water to form a smooth paste. Stir into soup until smooth. Add sugar and stir. Cool, chill, and serve cold, garnished with sour cream.