Position a rack in the lower third of the oven and preheat to 350 degrees . Using a food processor, finely grind the cookies. Drizzle the melted butter over the cookie crumbs and pulse briefly to mix. Transfer the crumbs to a 1-by-10-inch round fluted tart pan with a removable bottom. Evenly press the crumbs into the bottom and up the side of the pan. Bake the cookie crust until firm, about 10 minutes. Transfer to a rack to cool.
Meanwhile, reserve 1/2 oz. chocolate for grating on top, then coarsely chop the remainder. In a medium saucepan, melt the chopped chocolate and the remaining 8 tbsp. butter over low heat, stirring, until smooth. Remove from the heat and let cool for 5 minutes. In a large bowl, whisk together the eggs, 1 cup cream, the granulated sugar, vanilla and salt. Whisk the cooled chocolate mixture into the egg mixture until well combined.
Pour the filling into the crust and bake until set around the edge but slightly jiggly in the center, about 20 minutes (the filling will set as it cools). Transfer the tart to a rack and let cool completely.
When ready to serve, in a large bowl, combine the remaining 1 cup cream, the confectioners sugar and orange liqueur. Beat by hand or using an electric mixer until thick and billowy. Grate the reserved 1/2 oz. chocolate on top of the tart. Serve with the orange cream.