Onion Tarte Tatin is a savory twist on the classic French dessert. Caramelized onions are cooked with butter and sugar until golden and sweet, then topped with a flaky puff pastry crust. The tart is baked until the pastry is golden and crisp, and then inverted onto a serving plate to reveal the beautiful caramelized onions. This dish is perfect as an appetizer or a light lunch, and pairs well with a fresh green salad.