Line a 8x8 baking dish with aluminum foil or parchment paper. Set aside.
In a medium mixing bowl, combine the graham crackers crumbs, sugar and melted butter. Toss until all crumbs resemble wet sand.
Press the graham crumb mixture into the prepared baking dish. Place the crut in the freezer while making the filling.
In a separate medium mixing bowl, whisk together the vanilla pudding mix with 2 cups of the cold milk. Whisk until soft set (you start to feel some resistance while whisking.) Fold in 1 cup of the whipped cream. Pour the pudding mixture over the chilled graham cracker crust. Place it back into the freezer while making the next layer.
In the same bowl, whisk together the pistachio pudding mix and the remaining 2 cups of milk until soft set. Fold in 1 cup of the whipped cream. Pour the pistachio pudding layer over vanilla pudding layer, spreading evenly.
Cover with aluminum foil or plastic wrap and freeze for a minimum of 6 hours.
Finish with the remaining 1 cup of whipped cream.
Garnish the icebox cake with chopped pistachios, chocolate syrup and maraschino cherries. Store in the freezer until ready to serve.
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