To make the crust:
Preheat oven to 375 degrees F.
Grease pie pan.
Pulse Oreos in large food processor until coarse crumbs.
Add in sugar and butter and keep pulsing until completely combined.
Press into prepared pie dish.
Bake in preheated oven for 10 minutes.
Remove from oven and let cool.
To make the filling:
Combine chocolate, Nutella, and 3/4 cup heavy cream in double boiler or microwave safe bowl.
If using a double boiler: Melt chocolate, Nutella, and cream, stirring often.
If using a microwave: cook on high in increments of 30 seconds, stirring well after each interval. When it starts to get pretty melted, decrease intervals to 15 seconds, until completely melted.
In small bowl, whisk together remaining 1/4 cup cream, egg yolks, and vanilla extract.
Stir well into chocolate.
Pour into pie crust.
Cover and refrigerate for 2 hours.
To make the whipped topping:
Melt chocolate and Nutella in double broiler or microwave using method above.
In large bowl, beat heavy cream until soft peaks form.
Add melted chocolate/Nutella mixture and liqueur, and beat until stiff peaks form.
Spread evenly on top of pie.
Garnish with chocolate curls.