Follow the direction on the cake mix box to prepare the actual cake. Prepare it in a 9 x 13" pan. When golden, remove from over and let cool for a few minutes.
When just slightly cooled, use the end of a wooden spoon (the handle end) to poke holes into the baked cake. Don't be shy; make the holes big enough for the pudding to seep into and go deep enough with the spoon that you hit the bottom of the pan.
Next, prepare your pudding mixture. Combine your 4 cups of milk and the instant pudding mix; whisk until fully combined and there are no lumps.
Now it's time to fill those holes! Pour the pudding mixture ver the entire cake, taking care to get it into all your holes. Use the spoon to help really get it into the cake and spread evenly.
Refrigerate for apx two hours... or until set. Top with whipped topping, crushed vanilla wafers and sliced banana! Serve and enjoy. (Refrigerate any leftovers.)