Combine all ingredients in a food processor or blender and process until smooth. Transfer sauce to a covered container and chill for at least 24 hours to develop flavor. Serve drizzled over chilled cooked shrimp, or warm the sauce and toss with hot pasta.
Makes 4 servings.
A variation on pesto, this recipe combines parsley, watercress, and basil in a sprightly sauce for shrimp, salmon, carpaccio, or pasta.