In a bowl, make the pudding according to the package directions. Mix two cups of milk with jello pudding. Allow the pudding to thicken for 5 minutes.
In a separate bowl, whip two cups of heavy cream with ⅓ cup of powdered sugar until soft peak formed (or use cool whip).
Once the pudding thickened fold in two cups of whipped cream. Add 4 tablespoons of powdered pistachios to the mixture .
To assemble the cake: spread a thin layer of the mixture in an 8 x 8 pan to coat the bottom and then add a layer of graham crackers to the bottom of your pan.
Spread the cream mixture on top to cover the graham crackers and then sprinkle powdered pistachio on top.
Repeat the process until you have as many layers as desired. Then, sprinkle the last layer with powdered pistachios.
Refrigerate for at least 4 hours or overnight until the graham crackers are completely softened.