Preheat oven to 350 degrees F. Liberally grease a large bundt pan with cooking spray and set aside.
In a large bowl, combine the cake mix, pudding mix (just the dry mix), eggs, oil, buttermilk and sour cream with a handheld electric mixer on medium-low speed. Beat for 2 minutes or until combined and smooth. Pour into the prepared pan and smooth out the top.
Bake for approx. 45-55 minutes or until a toothpick or knife inserted near the center comes out clean. Cool completely before inverting onto a wire rack.
Once cake has cooled, make your ganache. In a large microwave-safe bowl, microwave the heavy cream and 1 cup of the semi-sweet chocolate chips for 45 seconds. Stir, then microwave for another 30 seconds or until melted and smooth. Allow the ganache to set at room temperature for about 15 minutes before pouring over the top of the cake. Garnish immediately with the miniature chocolate chips and let set, about 20 minutes. Cut into slices and serve!