Preheat oven to 350 degrees. Grease a bundt pan well. Set aside.
In a large bowl, combine cake mix, kosher salt and orange zest from 2 oranges. Set aside.
In another bowl, whisk together buttermilk, orange juice, oil, eggs, vanilla and sour cream. Pour into the dry mixture and fold until it just comes together. Pour into prepared bundt pan.
Bake for 35 to 40 minutes, until a toothpick comes out clean. Remove from oven and let cool for 5 minutes. Place a cooling rack on top of the cake and gently flip to release the cake from the bundt pan. Allow to fully cool.
Once cake is cool, make the ganache. Place chopped chocolate and orange zest into a bowl. Set aside. Add heavy cream to a small saucepan or microwave safe bowl. Bring to a simmer then remove from heat. Pour hot heavy cream over the chocolate mixture and stir until all the chocolate is melted. Pour over the cooled cake.