Grease a 9½ inch pie pan with butter or baking spray. Set aside.
No Bake Oreo Crust:
In a medium-size bowl combine melted butter with Oreo cookie crumbs and mix until fully combined.
Press the cookie crumbs mixture into the bottom and up the sides of the pie pan; using a measuring cup, press the cookie crumbs into the pie pan shape. Place in the fridge for the crust to harden.
No Bake Chocolate Pie Filling:
Add 1 cup of heavy whipping cream, the powdered sugar, and vanilla extract into the bowl of an electric mixer and whip on high until it begins to thicken and it holds its shape. Set aside.
Add chocolate, remaining ½ cup of heavy cream and butter to a microwave-safe bowl and microwave for 1 minute. Stir with a spatula and microwave for another minute, until the mixture starts to boil.
Add espresso powder and stir until the chocolate is fully melted and the mixture is smooth and shiny.
Whisk in the mascarpone cheese into the chocolate mixture until fully combined and smooth.
Fold the whipped cream into the chocolate mixture with a spatula, and stir until fully combined.
Pour chocolate mixture evenly into the chilled pie crust.
Garnish:
Add 1 cup of heavy whipping cream and the powdered sugar into the bowl of an electric mixer and whip on high until it begins to thicken and it holds its shape.
Add whipped cream to a piping bag fitted with the star tip and pipe whipped cream onto the pie.
Top with Oreo cookies, if desired sprinkle with cocoa powder.