In a large mixing bowl, beat the softened cream cheese with an electric mixer until smooth and creamy. This should take about 1-2 minutes.
Gradually add the instant pistachio pudding mix and the milk to the cream cheese. Mix on medium speed until well combined and the mixture begins to thicken, which should take about 2 minutes.
In a separate bowl, whip 1 cup of heavy cream until stiff peaks form. This will give your filling a light and airy texture.
Gently fold the whipped cream into the pistachio mixture using a rubber spatula. Be careful not to deflate the whipped cream; you want to maintain as much air as possible.
In another bowl, whip the remaining 1/2 cup of heavy cream with the powdered sugar until stiff peaks form. This will be used as a topping for your pie.
Pour the pistachio filling into the ready-made Oreo crust, spreading it evenly. Top with the sweetened whipped cream and smooth it out to cover the filling completely.
Refrigerate the pie for at least 4 hours, or until set. This allows the flavors to meld and the filling to firm up.
Before serving, sprinkle the top with semi-sweet chocolate chips and chopped pistachios for decoration and added crunch.
