Once cakes are cooled, use a serrated knife to carefully level cakes. Then carefully cut cakes in half. You may use a toothpick method. Mark top and bottom layer with a toothpick to mark where to stack cakes.
Whisk pastry cream briefly to make it easy to move.
Place first cake layer on a 12" cardboard round. Take a third of the pastry cream mixture using a spatula, spread evenly across the cake. Add next layer and repeat for next 2 layers.
Once the last layer is added to the cake. Gently press layer down and wiggle any layers to shape evenly. I usually leave a rounded piece on the top to give it some umph.
Take the 1 cup of cooled ganache and spread an even layer to coat the cake. This will be the crumb coat. Place cake in refrigerator for 4 minutes to let the chocolate stiffen up.
Set cake on top of a wire rack on a lipped baking sheet lined with parchment paper.
Mix the remaining chocolate ganache in the saucepan and begin to pour in a steady stream over the center of the cake. While pouring, begin to work your way out of the cake in a spiral until you cover the edges.
If the chocolate has stiffen too much and is not falling down the sides as expected, take a hair dryer to reheat the chocolate. Make sure you are not too close to the cake and are moving the hair dryer in fast sweeping motions all around the cake.
If the sides have not covered enough, take a long metal icing spatula and run it along the sides of the cake to cover it fully. If there are a lot of blemishes on the cake, do a quick once over with a hair dryer. Do this sparingly. You can also choose to pour the chocolate and intend not to fully cover the sides (making it a half naked cake).
Let the cake rest for 20-25 minutes before attempting to move.
Run the metal icing spatula under the cake to separate it from the wire rack before attempting to move the cake. Use the icing spatula to smooth out any lumps on bottom.
Decorate cake as desired and serve immediately. To store the cake, place in a cake box in the refrigerator. The chocolate may have some cracking if the pour was not thick enough. Serve at room temperature.