Preheat the oven to 375°F.

Set aside four whole gingersnaps for garnish. Process the remaining cookies in the bowl of a food processor until fine crumbs form, about 1 minute. Pour crumbs into a medium bowl and stir in the melted butter until evenly combined. Pulse the reserved gingersnaps in food processor to crush, then set aside in a small covered container for serving.

Generously butter a 9-inch pie pan. Dust with flour, shaking out any excess. Pour the crumb mixture into the pie pan and press along the bottom and sides to form an even crust.

Bake the crust on middle rack of oven until it begins to get a shade darker, about 10 minutes. The crust will look sunken, but will get its shape back as it cools.

Check to see that crust is done. Remove from oven or add time as needed.

Transfer the crust to a cooling rack and let cool completely, about 35 minutes.

Combine one quarter of the heavy cream, brown sugar, and spice in a small covered container. Refrigerate for up to one week (you'll use it for the topping). Place the remaining cream, brown sugar, spices, and the salt in a stand mixer bowl. Whip on medium-high speed until stiff peaks form when whisk is lifted, 2-3 minutes.

Place the pumpkin in a small bowl and stir in a few spoonfuls of the whipped cream mixture. Gently fold the mixture back into the remaining whipped cream until no streaks remain.

Pour the filling into the cooled crust and spread into an even layer. Freeze until firm, at least 4 hours or overnight. Once the pie is fully frozen, wrap in foil. The pie can be frozen for up to two weeks.

Uncover the pie and let stand at room temperature for 20 minutes. Pour the reserved whipped cream mixture into a stand mixer bowl. Whip on medium speed until thick. Transfer to a serving bowl.

Cut the pie into slices using a sharp knife. If needed, use a table knife to be sure you've cut all the way through the crust. Serve the pie with the whipped cream, caramel sauce, and the reserved crushed cookies to sprinkle on top.