Quite frankly old chaps I am amazed. I thought you may have pooh poohed the suggestion of this book, but I am sure you will love the outcomes - the flavours are magic and those of you old enough may recall the flavours when good quality BIRs first started. Some of the recipes are quite daunting as they seem to contain so many ingredients, but perservere.
You can modify some recipes as they were written in primitive times as it where so Mrs Singh didn't interfere with the originals too much to suit Western requirements. Example; she calls for Kachries in some recipes. They (their enzymes) are used for tenderising tough meats (the same enzymes were used by farmers in UK and Argentina prior to slaughter to tenderise the meat but this has been banned now). The Kachri is a type of knobbly green Papaya and can be bought in Asian Grocers and occasionaly - supermarkets like Tesco. I have tried using them and they do work and give a subtle taste to the meat. Anyway, enough of the waffle.
Now before I get asked, The Tandoori group of restaurants did have pots of (curry) bases because I was shown them, but I have no idea what their composition was. I suspect though they would be near Jaspers recipe as their bases were very mild but gently aromatic, they used a master base and two others I recall. The types of sauces I use now came from these chefs, i.e. the onion barga base, tomato and onion base, plain onion base, fresh tomato pulp; also the GMs and basic spice mixes; all of which may have been sourced from Mrs B S!
You won't get results like your common or garden High St BIR, I think they are much better and you will like them for sure. My book is covered in stains, especially where my favourites are!
Enjoy
CP