French Walnut Tart

This simple tart comes from the Perigord region of France, an area known for its walnuts. A cookie-like pastry shell is filled with the rich, subtly bitter nuts and buttery caramel. Our version tones down what is often cloying sweetness with a small measure of crème fraîche and a dose of cider vinegar (you won’t detect it in the finished dessert). Whole-wheat flour in the crust plays up the earthiness of the walnuts. To toast the nuts, spread them in an even layer on a rimmed baking sheet and bake at 325°F until fragrant and just starting to brown, about 8 minutes, stirring just once or twice; do not overtoast them or they will taste bitter. The dough-lined tart pan can be prepared in advance; after the dough has firmed up, wrap tightly in plastic and freeze for up to two weeks. The tart is superb lightly sprinkled with flaky sea salt and accompanied by crème fraîche or unsweetened whipped cream.