Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking pan.

In a large mixing bowl, combine the yellow cake mix, one box of instant pistachio pudding mix, and the crushed pineapple (juice included). Add the eggs and vegetable oil, then mix with an electric mixer on medium speed for about 2 minutes.

Pour the batter into the prepared baking pan and smooth it out evenly with a spatula.

Bake for 30-35 minutes, checking doneness around the 28-minute mark with a toothpick.

While the cake cools, whisk together the second box of instant pistachio pudding mix with the cold milk until it thickens, about 2-3 minutes.

Gently fold in the Cool Whip or whipped topping.

Spread the pistachio frosting over the cooled cake and refrigerate for at least 1 hour before serving.

Slice the cake into squares and enjoy!