1 stick unsalted butter, cut into cubes and chilled
3 tablespoons ice water
2 large Granny Smith apples—peeled, cored and thinly sliced
1/4 teaspoon cinnamon
In a food processor, combine the flour with 2 tablespoons of the sugar, the baking powder and salt. Add the butter and pulse until the mixture resembles coarse meal. Sprinkle the ice water over the mixture and process just until large clumps of dough form. Turn the dough out onto a work surface and form into a flat disk. Wrap the disk in plastic and refrigerate for 1 hour.
Preheat the oven to 375°. Line a baking sheet with parchment paper. Position a rack in the center of the oven. In a medium bowl, toss the apples with the remaining 6 tablespoons of sugar and the cinnamon.
On a floured work surface, roll the dough out to a 12-inch round and transfer it to the baking sheet. Arrange the apple slices on the dough, leaving a 2-inch border all around. Fold the edge over the apples, pressing lightly. Refrigerate the crostata until chilled, about 20 minutes.
Bake the crostata for 1 hour and 15 minutes, or until the dough is golden brown and the apples are tender and bubbling. Slide the parchment with the crostata onto a rack and let cool. Cut into wedges, transfer to plates and serve.
The crostata can be kept at room temperature for up to 8 hours. Rewarm to recrisp the crust before serving.