Add the Oreos to a food processor and blitz until fine crumbs form, then transfer them to a mixing bowl.
Melt the butter, then pour it over the crumbs and mix well to combine.
Press the crumbs into a 9-inch pie dish to create an even, solid crust.
Place the crust into the oven and bake for 8-12 minutes or until nicely set. Set the crust aside to cool.
Whisk together the espresso powder, cornstarch, sugar, salt, and cocoa powder in a large pot off the heat.
Next, whisk in the cream until completely smooth. Finally, whisk in the milk, vanilla extract, and egg yolks.
Place the pot over medium heat and whisk constantly for 5 minutes, allowing it to thicken.
Once the custard reaches a low boil, whisk vigorously for 1 minute, then immediately remove it from heat.
Add the butter and chocolate to the custard and whisk until completely melted and the mixture is smooth.
Pour the custard into the pie crust, and use a spoon to smooth the surface.
Place a piece of parchment paper directly on top of the filling and transfer the pie to the fridge to set for 10 hours. Once set, gently remove the parchment paper.
To make the topping, add the cream and sugar to a bowl and whisk until stiff peaks form. Spread the cream over the chilled pie.
Drag a sharp knife over the surface of the dark chocolate to create chocolate shavings, then sprinkle them over the pie.