Ingredients

　　1 cucumber, peeled, seeded, and diced fine (about 3/4 cup)

　　3/4 cup sour cream

　　3 tablespoons drained bottled horseradish, or to taste

　　1 teaspoon white-wine vinegar, or to taste

　　2 teaspoons minced fresh tarragon leaves, or to taste, plus a tarragon sprig for garnish

　　In a bowl whisk together the cucumber, the sour cream, the horseradish, the vinegar, the minced tarragon, and salt and pepper to taste and chill the sauce, covered, for at least 2 hours and up to 1 day. Transfer the sauce to a serving dish and garnish it with the tarragon sprig.