Prepare Pie Crust:
Preheat the oven to 350ºF.
Place vanilla wafers, pistachios, and sugar in a food processor and process until finely ground, with just a few larger pieces of pistachios remaining.
Melt butter in a medium pot. Add crumbs to the pot and mix together until completely combined.
Pour the crumbs into the pie plate and start pressing the ingredients up the sides of the pie plate to form the edges first. Once the edges are formed, work the crumbs down to evenly distribute into the bottom of the pie plate and pack it down into an even layer.
Bake in the preheated oven for 8 minutes, until lightly golden and fragrant. Or, you can freeze for 30 minutes for a no-bake pie option.
Make the Filling:
With an electric mixer using the whisk attachment, whip the heavy cream until stiff peaks form, about 3 minutes. Set aside.
Place the mascarpone and the sugar in the bowl for the electric mixer. Whip on medium speed until completely smooth, about 2 minutes, scraping down the bowl halfway through. Scrape down the sides of the bowl and add ricotta and orange zest. Mix together until just fully combined.
Add 1/3 of the whipped cream to the ricotta mixture and fold it in with a rubber spatula by hand until it is completely combined.
Add the remaining whipped cream to the bowl and gently fold it in, being careful not to deflate it.
Pour the filling in the crust and smooth over the top.
Place in the refrigerator to set up. It needs at least 4 hours chilling time, but preferably overnight. Or place in the freezer to set up.