Preheat oven to 350 degrees. For the Cake: Combine dry cake mix, dry pudding mix, mashed bananas, eggs, water, oil and vanilla in a large bowl and whisk together until completely smooth and well combined. Pour into a very well greased and floured large bundt pan. Bake for 45 minutes or until a toothpick inserted in the center comes out clean. Remove from oven and cool in pan for 15 minutes. Then, invert to a wire rack and cool completely. When cake is completely cool, make the ganache.
For the White Chocolate Ganache: Place white chocolate chips in a small bowl; set aside. In a separate small bowl, microwave heavy cream for 20-30 seconds or until it starts to bubble. Pour hot cream over chocolate chips and allow to sit for 5 minutes. Stir together until chips are melted and mixture is silky smooth. If the chocolate chips aren't completely melted, microwave the mixture for 15 seconds at a time until chips are melted. Pour ganache over cooled cake and garnish with sliced almonds, if desired. Allow glaze to set, slice and serve.