This recipe is another oldie but goodie, I think from an aunt who loved pistachios. Back in the day when Mom entertained frequently, this cake could be quickly put together from what were her pantry staples. The only trick is to use the largest Cool Whip you can find, both to ensure that the frosting isn’t grainy and to have enough for filling and topping. I’ve also served this cake for Easter because the color works so well for that occasion, too.