In a large bowl, combine pudding mix with milk. Stir and allow to thicken for 5 minutes.
Fold in the whipped topping.
In a 9x13 inch pan, arrange a layer of graham crackers (you might need to break a few to fit in the pan and cover).
Spread half of the creamy mixture over the graham crackers in an even layer, then arrange a second layer of graham crackers. Spread the remaining creamy mixture, followed by a third layer of graham crackers.
To make the chocolate ganache layer, In a saucepan, heat the heavy cream until steaming – do not let it boil. Remove from the heat, and pour in the chocolate chips. Let sit for two minutes, then stir until the mixture is completely smooth. Stir in the corn syrup and allow to cool to room temperature (at least 30 minutes).
Pour the cooled ganache over the cake, you can use an offset spatula to gently guide the chocolate to cover the cake.
Cover the cake, and chill in the fridge for at least 8 hours and preferably overnight before slicing and serving.