In a large bowl, use a hand-held mixer to beat the cream cheese and a splash of the milk until smooth.Note: Or you can use a stand mixer.
Gradually beat in the remaining milk and then 1/2 a cup of heavy cream. Once smooth, beat in the pistachio pudding mix and granulated sugar.
Transfer to the oreo crust and spread evenly. Place in refrigerator.
Using a hand-held mixer or stand mixer, beat the remaining 1 cup heavy cream until it starts to thicken. Add powdered sugar and continue to beat until thick.Spread on top of the pistachio mxture.Note: If you want to make the pie look more decorative, spread half the whipped cream on the pie and transfer the other half to a pastry bag fitted with a large star tip and pipe it in a ring around the outer edge of the pie like in my pictures.
Place the chocolate chips in a microwave-safe bowl and microvave at 20 second intervals, stirring in between, until melted. Place in a small plastic bag, snip the corner and drizzle on the pie.
Sprinkle pistachios around the outer edge.Refrigerate for at least 2 hours before serving.