Preheat the oven to 350° F. Butter an 8-inch springform pan or pie plate.In a food processor, pulse the cookies and butter together until you have fine crumbs. Press the mix into the prepared pan. Bake until golden, about 12-14 minutes.Meanwhile, make the filling. In a medium pot, whisk together the sugar, arrowroot powder (or cornstarch), cocoa powder, and salt. Whisk in 1/3 cup milk until a paste forms. Then, slowly whisk in the remaining milk until combined. Whisk in the egg yolks. Set the pot over medium-high heat and bring the mixture to a gentle boil. Cook, stirring continuously, until the mixture thickens and is pudding-like, 5-8 minutes. Watch closely. Add the chopped chocolate, hazelnut liquor (if using), and 2 teaspoons vanilla to a large mixing bowl. Strain the chocolate pudding mix through a fine-mesh strainer directly over the chopped chocolate. Stir until the chocolate is melted and the pudding creamy. Cover and chill 30 minutes to 1 hour.Using an electric mixer, whip 3/4 cup of cream until soft peaks form. Fold the whipped cream into the chocolate filling, then pour the filling into the crust. Chill 4 hours. Before serving, using an electric mixer to whip the remaining cream, maple syrup, and 2 teaspoons vanilla together until soft peaks form. Swirl the cream onto the pie. Slice and enjoy! The pie will keep chilled in the fridge for 2-3 days.