1. Preheat oven to 425 deg F and grease or spray a 6'' bundt pan with butter/oil spray and set it aside.
2. In a large bowl, combine both sugars, oil, yogurt, and buttermilk until blended. Add in eggs next and mix well using a beater or with hands. Now stir in vanilla, cinnamon and sweet potato puree.
3. Sift flour, baking soda, baking powder, and salt on wet ingredients and fold till combined.
4. Take a cup of batter out in a bowl. Mix cocoa and buttermilk in and fold in to form chocolate batter.
5. Pour sweet potato batter in the pre-prepared bundt pan. Next pour half of chocolate batter in. 3rd layer will be sweet potato batter again.
6. Layer with the remaining chocolate batter next. And finish off with sweet potato batter. Don't be afraid to fill your bundt pan to the top. The initial high temp. will not let the batter to overflow.
7. Bake for 45-55 mins or until the cake passes the toothpick test.
8. Allow to cool down for 15 mins in the pan. Then invert on a wire stand to cool down further. Top with chocolate glaze on completely cooled cake!