Cherry Pie

Adapted from Ad Hoc at Home, by Thomas Keller
2 tablespoons cornstarch
2 tablespoons water
7 cups sweet cherries, such as Bing, pitted
3/4 to 1 cup granulated sugar
1 tablespoon vanilla or almond extract
Basic Pie Crust
1 large egg, beaten
Granulated sugar for sprinkling (optional)
Combine the cornstarch and water in a small bow, stirring to dissolve the cornstarch. 
Put 5 cups of the cherries in a large bowl; set aside.  Put the remaining 2 cups cherries in a food processor and puree.
Combine the puree and sugar (3/4 or 1 cup depending on the sweetness of the cherries) in a medium saucepan, bring to a simmer over medium heat, and simmer for about 30 minutes, stirring often to prevent the bottom from burning, until the mixture has reduced to 1-1/4 to 1-1/2 cups.  Reduce the heat to medium-low and, stirring constantly, add the cornstarch slurry (remix the slurry right before adding).  Bring to a boil, stirring, and cook until the mixture becomes translucent again.  Remove from the heat, stir in extract, and let cool completely. 
Revove top and bottom doughs from the refrigerator.  Position one oven rack in the bottom of the oven and the other in the center and preheat the oven to 400 degrees.
Stir the puree into the whole cherries and pour into the pie shell.  If the top crust is too hard to shape, let it rest at room temperature for a few minutes.  Moisten the rim of the pie shell with some of the beaten egg.  Cover the filling with the top crust and press the edges together to seal with the tines of a fork.  Brush the top crust with the beaten egg and sprinkle with sugar if desired.  Using a paring knife, cut a few slits in the top of the pie for steam vents. 
Cover the edges of the pie with aluminum foil that has been sprayed with cooking oil spray (i.e. Pam) to prevent the edges burning.  Place pie on the bottom rack of the oven and bake for 20 minutes.
Lower the heat to 375, remove the foil from the pie, move the pie to the center rack and bake until the crust is golden and the filling is bubbling, 25-35 minutes. 
Transfer the pie to a cooling rack to cool.  The pie is best served 2-3 hours after it is baked, but it can be kept at room temperature the day it is baked or wrapped and refrigerated for up to 3 days.