Preheat the oven to 400°F (207°C).
Using a stand mixer with a paddle attachment, mix the flour, salt and butter on low speed for 2 minutes, slowly add ice water until the dough becomes a ball.
Transfer the dough to a lightly floured work surface and knead 2 or 3 times, just until it comes together. Pat the dough into a disk. On a lightly floured work surface, roll out the dough into a 16- to 17-inch (40cm to 43cm) round, about 1/4 inch (5mm) thick. Line a large baking sheet with parchment paper. Roll the dough around the rolling pin and transfer onto the prepared baking sheet.
Peach Filling: wash and, if needed, rub the peaches to remove any fuzz. Cut the peaches in half, remove the pits, and cut into thick 1-inch (2.5cm) slices. Place the peach slices in a large bowl and season with the salt. Then add 3 tablespoons sugar and gently toss to combine.
Arrange the peach slices on the pastry, placing them as close together without overlapping the slices too much. Leave about a two inch wide outside border. Gently fold the edges of the pastry up and over the peaches, pleating as necessary. Make sure to seal any cracks in the pastry.
Bake the tart in the center of the oven for 1 hour, or until the peaches are tender and golden and the crust is cooked through. Let the tart cool slightly before serving. Dust with powdered sugar, optional.