Place instant vanilla pudding and milk into a large bowl. Use a hand mixer (or whisk) to mix this together well.
Fold in the thawed whipped topping.
Cover the bottom of a 9X13 baking dish with graham crackers. Break them as necessary to completely cover the bottom. (Each layer should use about 1 sleeve of the graham crackers.)
Spread half of the pudding mixture evenly over this layer of crackers.
Use another sleeve of graham crackers to create another layer.
Spread the other half of the pudding mixture evenly over this layer of crackers.
Use the last sleeve of graham crackers to cover the pudding mixture.
Place chocolate chips, heavy cream, corn syrup, and vanilla into a medium sized microwave-safe bowl. Microwave for 1 minute. Stir. Continue cooking for 30 seconds at a time. Stirring each time. Once you are able to stir it smooth, allow it to cool for a few minutes. Then pour it over the eclair cake. Smooth the top with a spatula.
Cover the cake and place it in the refrigerator. It must chill for at least 8 hours. Overnight is preferable.