Preheat oven to 425F
In a large bowl add flour, baking powder, baking soda, brown sugar, salt., cinnamon, and nutmeg. Whisk to combine and break up lumps from brown sugar.
Add cold butter cubes and use a pasty cutter or fork to combine until you have pea sized crumbles. Set aside in the refrigerator.
In a separate medium bowl, combine sweet potato, buttermilk, and vanilla. Whisk until the mixture is smooth.
Combine your dry ingredients and sweet potato mixture. Mix until the flour is covered in flour.
Turn your dough out onto a floured work surface. Gently knead and push the dough together until your dough forms a smooth ball.
Pat the dough down into a 1 inch layer and cut out biscuits. (Here I'm using a 3" round cutter).
Place biscuits in your buttered pan or skillet. Beat egg well, and brush over each biscuit.
Bake for 15 minutes or until the tops are golden brown.
