Try the book:
Curry Secret by Kris Dhillon, changed my curries for the better.
Was told about this years ago, when I was using a very expensive book for recipies and every curry turned out not quite right.
Mate of mine told me about this - at the time £1.99 - paperback. I poo-pooed this, as I had a very expensive posh hardback book. Anyway, he bought the Curry Secret for me. Amazing stuff. What I had been doing with my expensive book was making Indian food. Very nice but not what we get in Blighty from a curry house.
I needed a book to show me how to make Indian Restaurant food.
There is a basic sauce which you make and can then freeze. I think the paperback is about a fiver now, but you can get a second hand one from the usual suspects.
Try it, you'll love it.
Barry