Preheat the oven to 350°F (175°C). Combine the cookie crumb base by mixing the crushed chocolate cookies with melted butter and sugar until the mixture is uniform and moist. Press this blend into the bottom and up the sides of a 9-inch pie plate. Bake for 8 minutes. Set aside to cool completely.

For the brownie filling, melt the butter and chopped unsweetened chocolate in a medium saucepan over medium heat, stirring until fully smooth. Take off the heat and immediately whisk in the sugar. Beat in the eggs one by one, mixing briskly to prevent scrambling. Add vanilla. Gently incorporate the flour, cocoa powder, and salt just until the batter is combined. Spread this mixture over the cooled crust and bake for 15 to 18 minutes, or until just set in the center. Let cool fully.

To prepare the pudding layer, whisk together sugar, cocoa, and cornstarch in a medium saucepan. Gradually pour in the milk, whisking until smooth and lump-free. Set the pan over medium heat and cook, stirring without pause, until the mixture thickens—approximately 6 to 8 minutes. Slowly whisk in the beaten egg yolks, then return to the heat for 2 additional minutes. Remove from the stove and mix in chopped semisweet chocolate, butter, and vanilla until melted and smooth. Cool slightly before spreading it evenly over the brownie layer. Place in the refrigerator for about 2 hours until set.

In a chilled mixing bowl, beat the cold cream, powdered sugar, and vanilla extract together until firm peaks develop. Smooth the whipped cream over the chilled pudding layer in an even coating.

Refrigerate the entire pie for at least 1 more hour prior to slicing and serving. If desired, adorn the top with curled chocolate, roasted pecans, or soft mini marshmallows to enhance both appearance and flavor.