For the chocolate apple pie cake: Preheat the oven to 350 degrees F.
Use the butter to grease the bottom and sides of a 9-inch cake pan or springform pan. Cut out a circle of parchment paper to fit the pan and place it on the bottom.
In a large bowl, prepare the cake batter as instructed on the box. Pour 1 cup of the batter into the cake pan and spread it out. Add the apple pie on top of the cake batter, then pour the rest of the cake batter over the top and around the sides. Spread it to make sure there are no air pockets.
Bake the cake until a toothpick inserted in the center and around the edges comes out clean, 50 to 55 minutes. Remove to a rack to cool slightly. When cool enough to handle, turn the cake out onto the rack, peel off the parchment paper and allow to cool completely.
For the ganache: Pour the chocolate chips into a medium bowl. In a small pot on medium heat, add the heavy cream, rum and a pinch of salt and whisk until warm. Pour over the bowl of chips and allow to sit and soak in for 2 minutes. Whisk to melt the chocolate completely.
Place the cake on a serving platter, pour the ganache in the center and spread gently outward over the edges. Sprinkle with the pecans and serve.