Ok, let me preface my comments with an acknowledgement that my recent experience of BIR fare is almost zero having given up on it not being anywhere near as good as it used to be when I most enjoyed eating BIR curry. So, yes, it's entirely possible that BIRs have started to use this method and I'm entirely unaware of it.
That said, when I was eating a lot of curry from different places, it was obvious from the taste and texture of the potato that all the restaurants and takeaways that I frequented used what must have been pretty identical cooking methods and that that method involved mainly boiling the potatoes after a quick stir fry in spices as I mentioned earlier.
Now I have been in a couple of kitchens where I have seen this being prepped, in pots about half the size of the base sauce pots, so I know it is the way it's done, but I wasn't in a position to question them about the ingredients etc. Further, just Youtube bombay aloo or similar and you'll see the method I've seen being demonstrated right there.
And, lastly, you want a home-sized quantity method? More than happy to oblige. This method, essentially the same as I have seen and the one I use, is from CBM and is on the forum somewhere:
For 2 lb of potatoes,
150 ml of veg oil
1 tennis ball sized finely chopped onion
1 tablespoon of garlic/ginger paste
Cassia bark 2" x 1" piece
1 bay leaf (Asian)
1 tablespoon of panch phoran
1 teaspoon of salt
2 tablespoons of tomato puree watered down 50/50
2 teaspoons of turmeric powder
1 tablespoon of mix powder
Water to cover
crackle whole spices in the oil
add onions and cook till translucent
add gg paste and cook until rawness is gone
add tom puree and spices, stir for a few seconds
add potatoes and stir around in the spices for a while
add water and simmer till done
Panch phoran
Cumin seeds
Fennel seeds
Nigella seeds
Fenugreek seeds
Mustard seeds
Preparation:
Mix all the above in equal quantities and store in an airtight container.
Other than the method, the panch phoran is the real key to this recipe and personally I double the quantity given. Also I use a lot of oil, to be spooned off later and used to start curries with, and then add enough water to just cover over the potatoes. The excess oil also reduces the evaporation of the added water so it doesn't dry out before the spuds are cooked. For me this ends up with perfectly cooked potatoes (slightly under done to allow further cooking later with practice) with a thick spice coating. Bloody delicious and with a flavour exactly as they used to be in the old days!