This rustic free-form tart is a beautifully delicious way to showcase sweet, summery peaches (or nectarines) and ripe, plump berries. We take a very minimalist approach to the filling and mix the fruits with only white sugar, grated lemon zest and a pinch of salt; we skip the spices and thickeners that blunt delicate floral flavors and aromas. The crust that encases the filling is especially high in butter, but it comes together with remarkable ease in a food processor and handles beautifully. After rolling the dough into a round, we dust the surface with a light layer of sugar, then invert the dough sugared side down onto the baking sheet. The sugar coating helps the pastry bake up with a shattering crispness that, along with its rich, buttery flavor, perfectly complements the succulent fruits. We especially like raspberries in this tart, but if you prefer, feel free to substitute blackberries or blueberries. And if you wish to change up the citrus, try orange zest in place of the lemon zest. Serve warm or at room temperature. Ice cream, gelato or lightly sweetened whipped cream are perfect embellishments.