Preheat the oven to 350°F (180°C), grease a 9-inch pie pan, and position it on a baking sheet.

Pulse gingersnap cookies into fine crumbs in a food processor. Add sugar and salt, then pulse to combine.

Combine crumbs with melted butter and check for the "clump test." Press the crust mixture into the pie pan to form an even layer.

Bake the crust for 8-10 minutes until lightly browned. Cool completely.

Mix sugar, cornstarch, salt, nutmeg, and cinnamon in a bowl. Add eggnog, cream, and rum in a pot. Whisk in the dry mixture until combined.

Heat the mixture over medium-low heat, stirring constantly, until thickened, approximately 3-5 minutes. Cook further until pudding reaches a "first boil." Stir for an additional 2-4 minutes until creamy.

Remove from heat and stir in vanilla extract. Fill the pie crust with the pudding mixture.

Cover the filling with plastic wrap and refrigerate for at least 4 hours, up to 24 hours.

In a mixer, whip heavy cream, powdered sugar, and vanilla extract until medium peaks form. Spoon whipped cream atop the pie.