On a lightly floured surface, roll out the chilled dough into a 14-inch round. Using a 9-inch pie pan as a template, place it rim down on the dough and cut out a circle about 2 inches larger than the rim with a pastry wheel. Slide a long metal spatula underneath the dough to loosen it. Fold the dough round in half, center it over the pie pan and open it. Gently press the dough against the bottom and sides of the pan without stretching it. The dough should drag on the table. Set the pie pan on a bowl to allow the edge to hang down; refrigerate for 30 minutes. Preheat the oven to 450 degrees. Place a piece of foil on the bottom of the oven to catch any drips.

Make the filling:

In a large bowl, whisk 2/3 cup of the sugar with the cornstarch. Gently toss in the peaches. Let sit for 10 minutes.

Meanwhile, remove the pie shell from the refrigerator. Gently toss the peaches. Let sit for 5 minutes longer. Combine the blueberries and raspberries and gently stir them into the peaches. Pour the fruit into the pie shell and distribute it evenly. Scrape in all the liquid and any undissolved sugar clinging to the bowl. When the dough is pliable, fold the overhanging edge to cover the outer portion of the filling, leaving a 5-inch opening of exposed fruit in the center of the pie.

Using a pastry brush, moisten the surface of the dough with cold water. Sprinkle the remaining 1 teaspoon sugar over the dough. Bake the pie on the lower rack of the oven for 20 to 30 minutes, until the crust begins to brown. Then lower the temperature to 375 degrees and bake for 35 to 45 minutes longer, until the fruit is bubbling and the crust is nicely colored. Transfer to a rack to

cool for at least 2 hours.