This is sort of a cheat and really simple.
1 yellow cake mix, bake as directed for a 9 x 13 sheet cake.
When done, take out of oven and poke holes all over it with a wooden skewer. I used a small can of crushed pineapple and poured the juice all over the cake, making sure to pour some down the holes. Then I spread the pineapple all over the top. Let cool to semi cool, sift confectioners sugar on top, then cover with saran. The sugar kind of melts into the juice since the cake is warm. If you cover while still warm, this helps the pineapple juice to continue to soak into the cake.
Cut a big piece, pour a glass of milk and enjoy.
That's it. Super easy, simple and yummy.