The day before serving, or early in the day prepare the crust and fill with ice cream.
Remove ice cream from freezer. Let sit on counter while preparing crust.
Crush Oreos in food processor.
Add 3 tablespoons melted butter while using the pulsing action on the food processor.
Press the crumbs into a 9 inch pie plate with deep sides, or a 9-10 inch springform pan or a 9x13 pan.
Spoon softened ice cream into prepared crust. Be careful to not press too hard or crust will separate.
Cover and store in freezer.
Place 1 cup whipping cream, 1/3 cup granulated sugar and 4 oz chocolate together over low heat in heavy pan, until chocolate melts.
Increase heat to medium and cook for about 8 minutes while stirring occasionally to prevent scorching. You may use a double boiler for this process!
Remove from heat and add vanilla, mixing until smooth.
Let cool completely before topping the ice cream.
When hot fudge is completely cooled, top ice cream and place pie back into freezer.
Whip cream in stand mixer or large bowl with hand mixer. Add 2 tablespoons powdered sugar to whipped cream, while beating on low, beat until stiff.
Top pie with whipped cream and remaining Oreo crumbs.
Store in freezer for at least 4 hours or up to 2 days before serving. Pie is best when allowed to sit in freezer for 6+ hours!