Preheat oven to 350 degrees. Spray a 13x9 pan with nonstick cooking spray and set aside.
Prepare cake according to directions.
Pour cake mix into a 13x9 pan and bake according to package directions.
In a medium saucepan, combine the sugar, cornstarch and salt.
Add in the milk and cream and stir to combine.
Heat the milk to just under a boil.
When small bubbles start appearing on the sides of the pan, it’s time to temper the eggs.
Take 1/2 cup of the milk and slowly whisk it into the egg yolks. The eggs are now tempered and ready to add the pudding.
Add the eggs to the pudding and cook for 3 minutes then remove from the heat.
Stir in the vanilla and the butter. Set the pudding aside to cool a little.
With the handle of a wooden spoon, poke a hole in the cake.
Pour the pudding over the top of the cake, guiding the pudding into the holes.
Place the cake in the refrigerator for 30 minutes.
Take 5 Oreos and crush the chocolate cookies into crumbs and stir them into the 8 ozs of cool whip.
Top the cake with the cool whip and return it to the refrigerator for another 30 minutes.
Just before serving, Crush the remaining 15 Oreo cookies and sprinkle them on top of the cake.
Garnish with a little chocolate syrup and serve immediately.