Preheat oven to ° Make crust: Butter and lightly flour a 9-in. sturdy metal pie pan. In a food processor, whirl cookies with sugar into fine crumbs. Drizzle in butter and whirl, scraping bottom of bowl occasionally, until crumbs come together.
Press crumb mixture evenly and firmly over bottom, up sides, and slightly higher than rim of pie pan (don't press over rim, or it will crumble when cut). Press rim firmly together. Run a spoon around bottom inner edge of pie, scooping away extra crumbs; otherwise the crust tends to get too thick.
Bake crust until firm and lightly toasted, 12 to 14 minutes. Let cool.
Make filling: In a large bowl, mash ice cream to an even consistency with a metal pastry blender or large fork. Stir in pie mix, then freeze 15 minutes.
Carefully dollop ice cream into center of cooled crust and spread outward, not quite but almost to edge (the ice cream will naturally settle outward to fill the crust). With a small metal spatula, swirl the top into waves if you like. Slide into freezer, making sure pie is level; otherwise it will freeze lopsided. Freeze at least 4 hours and up to 1 week (cover if more than 4 hours).
Up to 2 hours before serving, whip cream with sugar into soft peaks. Chill until ready to use.
A few minutes before serving, take pie out of freezer to soften. Cut into slices and top each with whipped cream and a big pinch of crystallized ginger.
Make ahead: Pie, up to 1 week, covered with plastic wrap and frozen. Whipped cream, up to 2 hours.
*Or use 1 cup canned puréed pumpkin mixed with 1/2 tsp. each ground cinnamon, allspice, and ginger, plus 1/4 tsp. each cloves and nutmeg.
Candied-Orange Walnut Ice Cream Pie: Use chocolate wafer cookies (such as Nabisco Famous brand) instead of gingersnaps in step In step 4, replace the pie mix with 1 cup diced candied orange peel (see sunset.com for a recipe, or use store-bought). Top pie with 1 cup Shiny Candied Walnuts: Whisk 1/2 cup confectioners' sugar, 1/4 tsp. salt, and 1/2 tsp. vanilla extract with 1 tbsp. water. Turn 1 cup coarsely chopped walnuts in sugar mixture to coat thoroughly. Spread on a parchment-lined baking sheet and bake at 300° for 12 minutes. Let cool. Right before serving, sprinkle on pie.
Toasted Almond and Chocolate Toffee Ice Cream Pie: Use amaretti (Italian almond cookies) instead of gingersnaps in step In step 4, replace pie mix with 1 cup crushed chocolate almond toffee. When pie is frozen solid, spread with a thin layer of Easy Chocolate Ganache: In 20-second bursts, microwave 1 1/2 cups semisweet chocolate chips with 1 tbsp. room-temperature salted butter, stirring after each burst, until mostly melted, about 1 minute. Let sit until melted, then whisk in 2 tbsp. whipping cream. Let cool. Top ganache-covered pie with toasted sliced almonds.