Heat oven to 425°. Place the pumpkin cut-side down on a baking pan, and roast until tender, 50 to 60 minutes.
Meanwhile, lightly dust a clean surface with flour, and roll out each circle of dough to a 14-inch diameter. Fit circles into the plates, being careful not to stretch the dough too thin; create the edges of your choice. Using a fork, prick the dough all over. Transfer to the freezer until firm, about 15 minutes. Remove pumpkin from oven, and set aside to cool.
Using a large spoon, scrape out and discard the seeds. Remove the flesh from the skin, and transfer it to the bowl of a food processor. Process until the pumpkin is completely pureed without any solid pieces, about 1 minute. Transfer 2 cups of the pumpkin to a large bowl. Add the sugar, cornstarch, salt, cinnamon, ginger, nutmeg, eggs, and evaporated milk, and mix well until well combined; set aside.
Fill pie shell with dried beans, and bake for 15 minutes. Remove beans and bake 5 minutes more. Remove pie crust from the oven. Reduce oven temperature to 350°.
Pour the pumpkin filling into the pie shell. Return to the oven to bake until all but the center is set, 40 to 45 minutes. (If the crust gets too dark, cover the edges with foil.) The filling will be slightly loose in the center but will firm up as it cools. Place on a wire rack until completely cool.
Serve the chilled pie with whipped cream.