Prepare the yellow cake mix according to directions on the box with ingredients needed to make cake listed on the box.
Once cake comes out of the oven, allow it to cool for just a couple of minutes.
Then, with a wooden spoon handle, begin poking holes in the cake. You want the holes to be big enough so that the pudding has plenty of room to get down in there. Also, make sure that you poke right down to the bottom of the cake.
In a bowl, whisk together the 2 packages instant banana pudding with 4 cups cold milk. Stir quickly until all the lumps are gone but before the mixture starts getting too thick to pour.
Pour pudding over cake. Be sure to pour the pudding right into the holes as much as possible.
Spread it all out and using the back of the spoon, gently push pudding down into the holes.
Put the cake into the refrigerator to set and cool (about 2 hours.)
Once the cake has completely cooled, spread on 8 ounce tub frozen whipped topping, thawed.
Sprinkle the crushed vanilla wafers onto the top of the cake before serving. Keep refrigerated.
