The Curry Secret, by Kris Dhillon. Published in 1996 by Elliot Right Way books. ISBN 0-7160-2054-8.
Buy from Amazon (link is for a new edition).
There simply is no other curry book like this one. If you are going to make a serious amount of indian dishes, and have freezer space / fridge space for pre-prepared sauces and meats, this book is the one for you. The results are simply delicious. From authentic-tasting tikka to aloo gobi and delicious Bhunas and Masalas.
The basis of all the curries in this book is the signature curry sauce that is pre-prepared. This part of the process entails much blending, boiling and simmering of onions, tomatoes, ginger, and garlic. The green proto-curry can be frozen in bulk and defrosted as needed, for best results bung it back through the blender once fully defrosted as it will separate a bit. I have not tried storing the finished curry sauce but that should refrigerate well. Once this is done, all the curries in this book take well under an hour from raw ingredients to finished curry on the table. This is their beauty, but the effort of making the sauce (and for lamb, pre-cooking the meat) in advance only pays off for special occaisions or if you are a regular curry-fiend.
The only recipe in this book I treat with scepticism is the chicken tikka. Just muse the tandoori marinade as for lamb tikka. Much nicer result (in my opinion, could have been my ineptitude when i first tried it). Also - unless this has been updated in the latest edition, what a British cook would call a Bell Pepper is called capsicum. I only realised this after an hour spent scouring Al Amin in cambridge for this mysterious vegetable...
But with only these two trifling quirks, it's a truly marvellous book, and for under a fiver for a cookery book just buy it and see for yourself.