Italian sweet and sour onions—called cipolline agrodolce—typically are small whole onions simmered with sugar and vinegar. But Ristorante Barbieri in Calabria uses sliced tropea onions, a variety that is a specialty of the region. We apply their technique to standard supermarket red onions. The slices are cooked briefly—just about 15 minutes—to soften them slightly. They will not reduce to a sticky, jammy consistency; these are not caramelized onions. Be sure to use a nonreactive skillet to avoid an interaction between the metal and the vinegar. Agrodolce onions are a great accompaniment to grilled or roasted meats, add them to an antipasto platter or use them in sandwiches or on pizza.