Wash the sweet potatoes thoroughly, peel them, boil, and mash.
Add sugar, milk, and butter to the mashed sweet potatoes and mix well.
Add eggs and mix again until well combined.
Sift in cake flour and baking powder, then mix.
Pour the batter into a cake pan and spread it evenly.
Bake in a 180°C oven for 35 to 40 minutes.
After cooling, decorate with powdered sugar or nuts as desired.