Toss the gingersnap crumbs with the melted butter, I like to use a fork. Toss until everything is evenly moistened.
Pat the crust into your buttered pie plate, pressing down evenly on the bottom and up the sides. You can use the bottom of a measuring cup to help flatten the crust. Put in the refrigerator while you continue with the pie.
pie
Blend together the cream cheese, pumpkin, brown sugar, spice, vanilla, and salt. I do this in a food processor because it purees everything super smooth and you can start with cold cream cheese. If you want to use a stand mixer or an electric mixer you will need to start with very soft cream cheese to avoid lumps.
Fold in the 2 cups of whipped cream or your tub of whipped topping until no streaks are left. Fold gently so as not to deflate your whipped cream.
Turn the mousse into your crust and spread out to the edges. You can give the surface a swirled effect, or smooth it out, that's up to you.
Cover with foil, tenting the foil so it doesn't mar the surface of your pie, and chill in the refrigerator for six hours or ideally overnight. You can pop it in the freezer to hasten the chilling if you need to.
garnish
When ready to serve garnish the top of the chilled pie with whipped cream or whipped topping and a sprinkle of grated nutmeg or pumpkin pie spice.
Notes
*Use a food processor to grind gingersnaps or place them in a baggie and use a rolling pin to crush them to a fine consistency.