I first ate aloo bonda on a trip to Jaipur, India, and loved them so much that I tried to make them when I returned to Hong Kong. My first attempt was so bad they went straight into the bin. I quickly realised that the secret behind a good aloo bonda is in getting the potatoes cooked correctly; if you dice them before boiling and mashing them, they get waterlogged, which makes the filling too soft and soggy.
Choose the right potatoes, too - use firm-fleshed varieties that mash up smoothly; don't use waxy "new" potatoes.
Scrub the potatoes but do not peel them. Put them in a pan of water and add enough cool salted water to cover them by about 2cm (⅞ in). Bring to the boil over a medium flame then cook the potatoes, uncovered, until they're just tender enough to be pierced with a fork. Drain them immediately then place them in one layer on a tray, slicing them in half so the steam can escape.
When the potatoes are cool enough to handle, strip off and discard the skins. Roughly mash the potatoes and set them aside.
Mince the ginger. Cut the banana chilli in half lengthwise and scrape out and discard the seeds, then finely mince the flesh. Finely dice the onion and mince the garlic. Stack the curry leaves, roll them into a tight cigar, then finely julienne them. Roughly chop the fresh coriander.
Heat 30ml (2 tbsp) oil in a skillet and when it's hot, add the cumin seeds and mustard seeds. Stir for about 30 seconds, or until fragrant (the mustard seeds might pop).
Add the ginger, chilli, onion and garlic and cook for about a minute. Stir in the turmeric, chilli powder, garam masala, curry leaves and potatoes, then season lightly with salt.
Stir the ingredients over a low flame for a few minutes, or until the potatoes are evenly seasoned. Transfer the mixture to a bowl and cool to room temperature. Taste the mixture for seasonings and correct if needed, then stir in the coriander leaves.
Shape the mixture into balls about 4cm (1½ in) in diameter and lay them on a tray. Refrigerate for about 30 minutes.
Make the batter by mixing the chickpea flour with the turmeric, chilli powder, salt and baking soda. Stir in 150ml (⅔ cup) of cold water to make a thick, smooth paste. Gradually stir in more cold water as necessary, to make a batter that thickly coats your finger.
Wash the pan used to cook the potatoes, then dry it. Pour in oil so it's at the depth of about 5cm (2 in). Place the pan over a medium flame and heat the oil to 180°C (350°F).
Dip the potato balls into the batter so they are completely coated, then place them in the hot oil. Fry them in batches; do not crowd the pan. After frying them for about a minute, turn them over so they cook evenly. Continue to fry until the aloo bonda are medium golden brown and the batter is slightly puffed. Drain them on paper towels and serve hot, with the chutney of your choice.