Mix the cake mix according to the directions on the package.
Bake according to the package in a 9x13 baking pan.
When cake is done after testing it with a toothpick that comes out clean, remove it from the oven.
Poke holes in it about an inch apart using the back of a wooden spoon.
Mix two boxes vanilla instant pudding with 4 cups milk until smooth.
Pour over the cake with holes poked in the cake.
Refrigerate for 2 to 3 hours until pudding is set.
Heat the butter and heavy cream in the microwave for 1 to 2 minutes. Do not let it boil.
Remove from the microwave and add the chocolate.
Allow the chocolate to stand for a couple of minutes then whisk it until smooth.
Whisk in the powdered sugar and vanilla until smooth.
Pour over the cake and pudding that has been refrigerated.
Refrigerate until chocolate ganache is set a couple of hours.