Prepare the oven and pan. Preheat the oven to 350°F. Lightly grease a 9x13-inch baking dish and set it aside.

Make the cake batter. Add the angel food cake mix, pistachio pudding mix, vegetable oil, eggs, and the entire can of crushed pineapple with its juices to a large mixing bowl.

Mix thoroughly. Beat the ingredients together until the batter is smooth and everything is evenly incorporated.

Bake the cake. Pour the batter into the prepared baking dish and spread it into an even layer. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.

Cool completely. Remove the cake from the oven and allow it to cool completely before adding the frosting.

Prepare the pistachio frosting. In a mixing bowl, whisk the second box of pistachio pudding mix with the whole milk until the mixture begins to thicken.

Add the whipped topping. Gently fold the thawed Cool Whip into the thickened pudding until smooth, fluffy, and evenly combined.

Frost the cake. Spread the pistachio frosting evenly over the completely cooled cake.

Chill. Cover the cake and refrigerate it for at least 2 hours before serving.

Garnish and serve. Sprinkle chopped pistachios over the top just before serving, if desired. Slice into squares and serve chilled.