Ingredients

• white and pale green parts of 3 leeks (about 3/4 pound), chopped, washed well, and drained
• 1 1/2 tablespoons olive oil
• 1 small boiling potato (about 1/4 pound)
• 1 1/2 cups chicken broth
• 1 1/2 cups cold water plus additional to thin soup
• 1/2 cup shelled fresh or thawed frozen peas
• 1/4 pound sorrel*, stems discarded and leaves washed, spun dry, and cut crosswise into thin strips (about 3 cups loosely packed)
• 1/3 cup sour cream
• 1 teaspoon fresh lemon juice, or to taste
• Garnish: chopped hard-boiled egg and thin strips of sorrel
• available seasonally at some supermarkets and specialty produce markets

Instructions

1. In a large saucepan cook leeks in oil with salt and pepper to taste over moderately low heat, stirring, until softened. Peel potato and cut into 1-inch cubes. Add potato, broth, and 1 cup water to leeks and simmer, covered, about 10 minutes, or until potato is tender. Stir in peas and simmer, uncovered, about 5 minutes, or until peas are tender.
2. In a blender purée potato mixture with sorrel in 2 batches until very smooth, transferring to a bowl. Whisk in sour cream and remaining 1/2 cup water, adding additional to thin soup to desired consistency. Chill soup, covered, at least 2 hours, and up to 24.
3. Just before serving, stir in lemon juice and salt and pepper to taste. Garnish soup with egg and sorrel.