Preheat oven to 350 degrees F. Lightly grease a 9-inch pie pan and set aside.
In a medium bowl, combine the cookie crumbs, 2 tablespoons of sugar, a pinch of salt, and the melted butter. Pour the crumb mixture into the prepared pie pan and press the mixture evenly into the bottom and up the sides of the pan.
Bake the crust for 15 minutes, or until golden brown. Allow crust to cool completely.
Place the chopped chocolates in the top of a double-boiler, or in a metal bowl set over a pot of barely simmering water, stirring until melted and smooth. Remove from the heat.
Beat the egg yolks in a small bowl.
Combine the sugar, cornstarch, and 1/4 teaspoon salt in a medium saucepan over medium heat. Slowly add the milk in a steady stream, whisking constantly. Bring the mixture to a boil, whisking constantly to keep lumps from forming. Remove from the heat.
Slowly add 1/2 cup of the hot milk mixture to the yolks and whisk until smooth. Add the beaten yolk mixture to the remaining hot milk mixture and bring to a simmer over medium-low heat. Simmer, whisking constantly, until thick and smooth, about 3 minutes. Remove from the heat. Place a fine wire-meshed strainer over the bowl with the melted chocolate, and pour the pudding mixture into the strainer. Strain the pudding into the chocolate. Add the diced butter and 1/2 teaspoon of the vanilla to the chocolate and pudding mixture, and whisk until smooth. Add the marshmallows and stir to combine. Place a piece of plastic wrap directly on the surface of the pudding, to prevent a skin from forming. Refrigerate until pudding is set and completely chilled.
Place cream in the bowl of an electric mixer and whisk until soft peaks form. With the machine running, add the confectioners' sugar and remaining 1/2 teaspoon of vanilla. Continue whisking until stiff peaks form.
Fold 1/4 cup of the whipped cream into the chilled pudding. Fold in the walnuts and diced brownies.
Pour pudding filling into the pie crust and chill 30 minutes, or until ready to serve. Just before serving, top the pie with the remaining whipped cream and sprinkle with chocolate curls, if desired.
Yield: 1 (9-inch) pie, 6 to 8 servings
* Place shortbread cookies in a food processor and process, stopping to scrape down the sides as needed.