Boil the sweet potatoes, let them cool, peel, and mash them.
In a bowl, mix eggs and sugar together.
Add the mashed sweet potato, melted butter, and vanilla extract, and mix well.
Sift in cake flour and baking powder, then gently combine.
Pour the batter into madeleine molds.
Bake in a preheated oven at 180°C (356°F) for 15 minutes.