In a large saucepan heat olive oil over moderate heat and cook leeks until softened. Add potato, chicken stock, and water to the leeks and simmer, covered, about 10 minutes, or until potato is tender. Stir in peas and simmer, uncovered, for about 5 minutes or until peas are tender.
In a blender puree the soup in batches with the sorrel until very smooth, transferring to a bowl. Whisk in the sour cream and additional water, if necessary, to achieve desired consistency. Chill soup, covered, for at least 2 to 3 hours and up to 24 hours.
Before service, taste soup and adjust seasoning with lemon juice, salt and pepper.
In a skillet heat vegetable oil over moderately high heat and fry julienned leek in oil until golden brown. Transfer frizzled leeks to paper towels to drain.
In a small bowl whisk together sour cream and milk and transfer to a plastic squeeze bottle or a sealable plastic bag.
To serve, ladle soup into serving bowl. Drizzle sour cream mixture in a decorative pattern from the plastic squeeze bottle or from a corner of the sealable plastic bag that has been snipped off with scissors. Garnish soup with frizzle leeks.
Recipe courtesy of Gourmet Magazine