Prep the Oven & Pan: Get your oven ready by preheating it to 350°F (175°C). Lightly grease a 9x13 inch baking pan and set it aside.
Whip Up the Cake Batter: In a large mixing bowl, combine the white cake mix, the first package of dry instant pistachio pudding mix, vegetable oil, eggs, almond extract, and the entire can of undrained crushed pineapple. Mix on low speed for about 30 seconds, then scrape down the sides of the bowl. Increase the speed to medium and continue mixing for another two minutes until the batter is smooth.
Bake to Perfection: Pour the prepared cake batter evenly into your greased baking pan. Bake in the preheated oven for 35-37 minutes, or until a toothpick inserted into the center of the cake comes out clean. Once baked, remove the cake from the oven and let it cool completely on a wire rack.
Prepare the Light Frosting: Once the cake is fully cooled, it's time for the frosting! In a medium mixing bowl, whisk together the milk and the second package of dry instant pistachio pudding mix for 2-3 minutes, until the pudding mix dissolves and the mixture begins to thicken. Let it sit for a few minutes.
Fold in Whipped Topping: Gently fold in the thawed whipped topping until it's fully combined with the pudding mixture and no streaks remain. This creates a light and fluffy frosting.
Frost & Chill: Spread this delicious, airy frosting evenly over the surface of your completely cooled cake. For the best texture, pop the cake into the refrigerator for at least two hours before serving. This allows the frosting to set up beautifully.
Serve & Enjoy: If you like, sprinkle some chopped pistachios over the top before slicing and serving this delightfully easy and refreshing dessert!