4 tablespoons unsalted butter, at room temperature
1 cup heavy cream, chilled
1 tablespoon confectioners' sugar
How to Make It
Make crust: Preheat oven to 350ºF. Place cookies and salt in a food processor and blend until cookies are ground. Pour in melted butter and pulse until crumbs are moistened. Transfer to a 9-inch pie dish and press crumbs evenly over bottom and up sides to form a crust. Bake for about 15 minutes, until firm. Let cool on a wire rack.
Make filling: In a small cup, combine vanilla and espresso powder until coffee has dissolved. Mix 1 cup half-and-half with both chocolates in a saucepan and place on stove over medium-low heat. Cook, whisking often, until chocolates have melted and mixture is hot, about 5 minutes (it may look grainy). In a large bowl, whisk together sugar, cornstarch and salt. Pour remaining cup of half-and-half into sugar mixture and whisk until no lumps remain. Whisk in yolks.
While whisking cornstarch mixture constantly, slowly pour in hot chocolate mixture. When both mixtures are combined, pour back into saucepan, place on stove over medium-low heat and cook, whisking constantly, until thickened and beginning to boil, 5 to 7 minutes. Pour hot pudding into a clean medium bowl, and stir in butter and reserved vanilla-coffee mixture. Cover with plastic wrap, pressing plastic directly onto surface. Let pudding cool at room temperature for 1 hour, then pour into pie shell, cover with a fresh piece of plastic wrap and refrigerate at least 3 hours.
Make topping: A half hour before you're ready to serve the pie, pour heavy cream and confectioners' sugar into a chilled bowl and beat with an electric mixer at medium-high speed until firm peaks form. Remove plastic from pie and spread whipped cream on top. Refrigerate for 30 minutes, then slice and serve.