Boil the sweet potatoes, peel, and mash them.
Melt butter and dark chocolate using a double boiler.
Add the melted chocolate, butter, sugar, and eggs to the mashed sweet potatoes and mix well.
Sift in flour, cocoa powder, and baking powder, then mix evenly.
Add Hershey chocolate chips and mix into the batter.
Pour the batter into a pan and spread evenly.
Bake in a preheated oven at 180°C for 25 minutes.
Let cool, then cut into serving pieces.