Preparation Boil vinegar with sugar and 1/4 teaspoon salt in a small heavy saucepan, stirring, until reduced by half, about 3 minutes. Transfer to a cup. Wash leeks and pat dry. Cook in oil with 1/4 teaspoon salt in cleaned saucepan over medium heat, stirring occasionally, until softened, about 5 minutes. Arrange frisée and pear on plates. Drizzle with hot leeks in oil, then vinegar reduction. Grind pepper over salads.
Preparation Boil vinegar with sugar and 1/4 teaspoon salt in a small heavy saucepan, stirring, until reduced by half, about 3 minutes. Transfer to a cup. Wash leeks and pat dry. Cook in oil with 1/4 teaspoon salt in cleaned saucepan over medium heat, stirring occasionally, until softened, about 5 minutes. Arrange frisée and pear on plates. Drizzle with hot leeks in oil, then vinegar reduction. Grind pepper over salads.