Make the crust: Preheat the oven to 350˚ F. Combine the cookies, granulated sugar and salt in a food processor. Pulse until finely ground, then add the melted butter and pulse again until the mixture looks like wet sand. Transfer to an 11-by-17-inch rimmed baking sheet and press the mixture evenly into the bottom and up the sides. Bake until set and crisp, about 12 minutes. Transfer to a rack and let cool completely.
Make the filling: Place the chocolate in a large bowl. Heat 1 cup heavy cream in a small saucepan over medium heat until steaming. Pour the cream over the chocolate and let stand until most of the chocolate melts, about 10 minutes, then gently stir until smooth. Spread the chocolate evenly over the bottom of the crust; let set, about 10 minutes.
Meanwhile, whisk 2 1/2 cups heavy cream, the pumpkin puree, granulated sugar, eggs, pie spice, vanilla and salt in a large bowl. Strain through a fine-mesh sieve into a separate bowl and pour over the chocolate layer. Bake until the pumpkin is set around the edges and puffs slightly in the middle, about 25 minutes. Transfer to the rack and let cool 20 minutes, then refrigerate until completely cooled, at least 2 hours.
Make the topping: Beat the remaining 3/4 cup heavy cream and the confectioners' sugar in a large bowl with a mixer on medium-high speed until stiff peaks form. Cut the pie into 15 squares. Dollop some whipped cream onto each square and sprinkle with crushed cookies.