How to Make It
Preheat oven to 425°F. Roll piecrust into a 12-inch circle on a lightly floured work surface. Fit into a 9-inch deep-dish pie plate; fold dough edges under, and flute. Prick bottom of crust lightly using a fork. Line crust with parchment paper; fill with pie weights. Bake in preheated oven until firm, about 10 minutes. Remove pie weights. Continue baking until crust surface is dry, about 5 minutes. Remove from oven. Reduce oven temperature to 375°F.
Whisk together eggs, sweet potatoes, brown sugar, butter, vanilla, zest, and cinnamon in a bowl until smooth. Gradually whisk in evaporated milk and 1 tablespoon of the bourbon until blended. Pour mixture into prepared crust. Bake at 375°F until pie is set, about 50 minutes. Let cool on a wire rack until completely cooled, about 1 hour, 30 minutes.
Beat heavy cream in an electric mixer fitted with a whisk attachment on medium-high speed until foamy, about 2 minutes. Add granulated sugar and remaining 1 tablespoon bourbon; beat until soft peaks form, 1 to 2 minutes. Serve with pie.
To make mashed sweet potatoes: Wrap unpeeled sweet potatoes individually in aluminum foil. Arrange on a baking sheet, and bake at 400°F for 1 hour. Let cool 15 minutes. Remove and discard sweet potato skins. Process sweet potato flesh in a food processor until smooth, about 1 minute.