Wash the sweet potatoes thoroughly, peel them, and cut them into small pieces.
Steam the sweet potatoes and mash them.
To make the sweet potato cream for topping, mix mashed sweet potato with heavy cream and sugar.
Cream the unsalted butter and sugar together in a bowl.
Add the eggs one at a time, mixing after each addition.
Sift the cake flour and baking powder, then quickly mix them in.
Add the mashed sweet potato and milk to make the batter.
Pour the batter into a mold and bake in a preheated oven at 170°C (338°F) for 30-35 minutes.
After baking and cooling, decorate with sweet potato cream on top.