Preheat oven to 350 F. Spray a 13 x 9″ baking dish with cooking spray or grease with shortening.
Combine flour, chopped pecans and butter in a medium bowl until combined. (Use a stand mixer to make this easier.)
Press flour mixture into the prepared baking dish, just covering the bottom. Bake for 15 minutes in preheated oven. Let cool completely.
Combine the cream cheese, half the Cool Whip, and powdered sugar together in another medium bowl until completely combined. (Mix by hand or with electric mixer.) Spread cream cheese mixture carefully over cooled crust.
Make pistachio flavor pudding according to package instructions, and spread over the cream cheese layer. Place in refrigerator for 5-10 minutes to let pudding firm up before going to next step.
Make vanilla pudding according to package instructions, and spread that over the pistachio layer. Again, place it in the refrigerator for 5- 10 minutes to allow the pudding to set.
Once your final pudding layer has finished setting up, top with the final container of Cool Whip. Garnish with chopped pecans if desired.
Keep refrigerated. Will keep for one week!
Ariane’s tip: To make it easier to spread the cream cheese mixture, dip your spoon in hot water as you go along.