Here is my theory on the use of potato in bhajis.
As I have previously stated, in order to get a perfectly cooked bhaji you need to allow the oil to penetrate to the middle of the bhaji. If you have too much thick batter, the onion in the middle is essentially stewing in the batter as the oil is not getting into contact with it. As Dipuraja showed and IG confirmed, in order to do this the onions need to be as firm as possible - not soft as a lot of us (myself included) previously thought. Any ideas of pre cooking the onions or salting them 24 hours beforehand went out of the window.
I hope you are with me so far as this is an essential fact to cooking good bhajis.
So in order to achieve 'airy' bhajis we now know we need to add salt at the last second, chuck in an egg to make the onions sticky, and then add just enough gram flour to coat the onions. We could in theory then form the bhajis and cook and I'm sure the results would be okay but there wouldn't be very much substance in the middle of the bhaji - only onion. By adding some very thin potato matchsticks to the mix (mine are usually even thinner than matchsticks) you can keep the bhaji loose and airy to allow it to cook through, while at the same time the potato breaks down after 5 or 6 minutes to form the soft centre. You certainly wouldn't know they contain potato even though you just made them.
I don't think this is a new thing and I certainly don't think it is a regional thing either. We have heard from chefs in Bristol, Sussex, Surrey, Hampshire and Newcastle. They all agree.
This will be my last post on the subject. If anyone is to stubborn to embrace this breakthrough then you deserve to wallow in bhaji mediocrity. Gaz, Axe and I (to name but three) demand perfection and it would seem we have all achieved it.