Make the crust-

Preheat oven to 350°F.                                      

In the bowl of a food processor, pulse the ginger snaps, sugar, and salt until very fine. Drizzle in 4 tablespoons of the melted butter until evenly disbursed, adding up to 1 additional tablespoon of butter if needed to moisten all the cookie crumbs.

Transfer gingersnap mixture to a 9-inch pie plate and arrange in an even layer, pressing firmly to form a crust.

Bake at 350°F for 8 minutes. Remove from oven and let cool while making filling. (Turn off oven as the filling will not require baking.)

Make the filling-

In a small bowl, sprinkle the gelatin over the cold water and let absorb for 5 minutes.

In a medium saucepan, whisk together the granulated sugar, cornstarch, salt, nutmeg, and cinnamon. Add eggnog gradually, whisking until smooth. Bring mixture to a boil over medium heat, whisking frequently. Continue boiling for 2 minutes until thickened. Add the gelatin and whisk until melted. Turn off heat and add vanilla and bourbon, stirring to combine.

Pour filling mixture into prepared crust. Cover surface with plastic wrap to avoid a skin from forming. Let cool to room temperature before refrigerating at least 4 hours or overnight.

Prepare the whipped cream (just prior to serving)-

In the bowl of a stand mixer fitted with the whisk attachment, combine the heavy cream, sugar, cinnamon, and vanilla. Beat on medium-high speed until medium peaks form.

Dollop whipped cream on top of pie and dust with additional cinnamon or nutmeg, if desired.

Serve immediately.