Volume 1 of Samaithu Par (Cook And See) by Meenakshi Ammal. My dog-eared copy is one of my most valued treasures and I still refer to her books after 27 years!
I used about 10 small potatoes, and got roughly petite bondas. We felt this size was perfect for them.
You can make them bigger, but these were fun-sized.
The batter should be neither too thin (won't coat properly), nor too thick (you'll get a heavy outer cover which will make the stuffing taste underwhelming). Add water little by little when making the batter.
You can reduce the chili powder in the batter if you want a milder blander cover.
These make a great party snack, and aren't too difficult to make. Have fun, eat them hot!
The same filling, if made a little less dry and more like a semi-solid, can play the role of masala filling for dosa, and masala accompaniment for pooris!