Pressure cook the sweet potato and peel and mash it really well and keep aside ( you can also puree the cooked sweet potato if you want)
In a bowl, mix the dry ingredients together - flour, cocoa powder, baking powder, baking soda and salt
In another bowl, beat the eggs and add sugar and melted butter, mix everything well.
In a small bowl, beat the yogurt really well so that there are no lumps, and then add 1/ cup of water to the smooth yogurt and mix well.
Add the yogurt water mixture to the mashed/pureed sweet potato and mix everything together.
Combine the sweet potato - yogurt mixture to the eggs-butter-sugar mixture and stir all the wet ingredients together.
Now slowly combine the wet ingredients mixture to the dry ingredients mixture and gently stir everything together.
The cake batter looked little thick to me, so I added the extra 2 teaspoons of water to the batter.
Preheat the oven to 350 degree Fahrenheit.
Grease the cake pan with butter and pour the batter.
Bake the cake for about 50 to 55 minutes or until a toothpick inserted in the center comes out clean.
The top of my cake got baked really fast at around 30 minutes, so I covered the top using an aluminium foil and then continued baking (I did it because the inside was not cooked but the top was cooked. So make sure you check your cake at around 3 minutes, and see if the top is already cooked so you can cover it with aluminium foil and continue baking.) Allow the cake to cool in the rack before you cut and serve!