For the potato filling:
Cook the potatoes and set aside.
Heat the oil in a frying pan, add the curry leaves, mustard seeds and cumin seeds and let them pop.
Add the finely chopped green chilli and then stir fry the diced potatoes, the turmeric, salt to taste, and some red chilli powder if you want it to be spicier.
Finish off with a squeeze of fresh lemon juice, then roughly mash the mixture and set aside to cool (make sure you are happy with the taste, adjusting salt, lemon and chilli to personal preference).
For the batter:
Mix all the ingredients in a bowl with luke warm water, a little at a time, enough to form a cream like consistency (like pancake batter). Adjust spice until you are happy with how it tastes.
If you can, make the batter the day before and leave it in the fridge, it's better. Just before cooking, add a pinch of soda bicarbonate or a teaspoon of Eno's fruit salts to the mixture (this is key to a light, aerated batter).
To make the vadas, take the cooled potato and make small balls from it, around 1 inch diameter. Put in the fridge to cool for half an hour.
Heat a couple of inches of good oil (like peanut oil) in a frying pan until hot.
Dip each potato ball in the batter until coated, then drop into the hot oil. Fry, ensuring all sides are coated with oil, for a few minutes until golden. Depending on the size of the pan, aim to fry 3-5 balls at any one time. Remove from pan and rest on some kitchen towels to absorb excess oil.
Serve the batata vada fresh and crispy, with more fresh lemon to squeeze over and a pinch of salt.
And most of all, enjoy! With beer!
Serve with the red and green chutneys on this site.