Preheat your oven to 350 degrees F.
Wash your potatoes thoroughly, place them in a baking dish and bake for 1 ½ to 2 hours or until tender.
Once the sweet potatoes are cooked, peel them and scoop out 1 ½ cups of the sweet potatoes, mash them and sit them to the side to cool. (Leave your oven pre-heated to 350 degrees while preparing your cake.)
In a separate bowl, whisk the baking powder, salt, cinnamon, nutmeg and flour together. Sit it to the side.
Using a hand or stand mixer cream the butter, brown sugar, and granulated sugar together just until light and fluffy (approximately 5 minutes).
Add the eggs to the bowl one at a time, mixing until combined before adding the next egg.
Add the vanilla extract and cooked sweet potatoes and mix until combined.
Add the flour mixture ½ c to 1 c at a time on low speed until combined alternating with the buttermilk- beginning and ending with the flour.
Using a spoon or spatula scrape down the sides of the bowl and mix ensuring that the batter is fully mixed together.
Spray a 12-cup bundt pan with baking spray.
Pour the batter into the pan and spread it evenly.
Bake for an hour and to an hour and 10 minutes. The cake is done once an inserted toothpick comes out clean.
Remove the cake from the oven and allow it to cool for about 20 minutes before removing it from the pan. Allow the cake to continue to cool on a wire rack before adding the icing.
To make the icing:
Using a hand or stand mixer, mix the butter and cream cheese until well blended.
Then add the vanilla extract and salt.
Next on slow speed, add the powdered sugar about a ½ c at a time until well blended and creamy.
Then add the milk and mix until combined.
Decorate the cake with the icing however you desire. Top with chopped pecans (optional) and serve.