In a mixing bowl, combine the softened butter, chopped pecans, all-purpose flour, and 1 cup of powdered sugar. Mix until well combined.
Press this mixture into the bottom of a 9x13 inch baking dish to form an even crust.
Bake at 350°F (175°C) for about 15 minutes or until lightly golden. Allow it to cool completely.
In another bowl, beat the softened cream cheese with 1 cup of powdered sugar and vanilla extract until smooth and creamy.
Gently fold in 8 ounces of whipped topping until well combined.
Spread this mixture evenly over the cooled crust.
In a separate bowl, whisk together the evaporated milk and the two boxes of instant pistachio pudding mix.
Beat until the mixture thickens, about 2 minutes.
Gently fold in another 8 ounces of whipped topping until combined.
Spread this pistachio pudding layer over the cream cheese layer in the baking dish.
Top the dessert with the remaining whipped topping, smoothing it out evenly.
Sprinkle the chopped shelled pistachios and chopped pecans on top for garnish.
Cover the dish with plastic wrap and refrigerate for at least 4 hours or overnight for the best results.