Add the pistachios and almonds to the bowl of a food processor and pulse until the nuts resemble crumbs. Add the sugar and pulse to combine. With the processor running, drizzle in the melted butter and pulse until combined. The mixture should stick together when pressed together.
Pour the crumbs into a pie dish and press along the bottom and up the sides to form the crust. (Note 2)
Refrigerate while preparing the filling.
Add instant pudding and milk to a bowl and mix until well combined. Add the marshmallow cream and mix until combined. Set aside.
In a separate mixing bowl, add the heavy cream and whip until stiff peaks form. Fold the whipped cream into the pudding mixture.
Pour into the pie crust and freeze until firm. Approx. 4 hours, or overnight. (Note 3)
To serve, slice and garnish with chopped pistachios or a drizzle of chocolate syrup and a cherry.
If using unsalted nuts, I suggest adding a pinch or two of salt to the crust mixture.
Use the flat bottom of a measuring cup or glass to press the crumb mixture firmly into the pie dish. This also helps to push the crumbs up the sides. The result is a smooth, compact crust.
For a softer pie, freeze for just 2 hours. The pie will have a soft, creamy consistency.