a bit of relevant intro:
the difference between success and fail must have very small margins. i've just made 4 off madras curry sauces. the 1st was a clear fail. i put this down to too little tomato puree (used 2 tbsp my norm but forgot the base i'm currently using has no tomato in it) and too much onion paste (used just over 2 tbsp). in pushing the stove & pan more (reduced the amount of water added to the tom puree) i almost burnt (family advised that these curry's don't smell good when they're cooked - must admit it did smell bad.
having learnt my mistakes the next 3 off went like a dream.
back to the onion paste.
after no 1 distaster i made 3 off identical madras curry sauces. each spot on. the onion paste works very well for me and my quest is over. i see very little chance of further fine tuning without inside knowledge.
the amount of onion paste added is critical. it needs to produce a subtle taste without the dish becoming out of balance. i added after the base had gone in
many thanks to Panpot for raising this post - i need to do a side by side comparison with BIR TA but feel my take is now as close as it needs to be - i feel i can now convert the madras curry sauce into a chicken madras dish.
the recipe for info: 300ml base, 2 tbsp yellow oil, 1.5 tbsp fine chopped garlic, 3 tbsp tom puree (2 tbsp if no tomato in base, with added water to runny consistency), 1/4 tsp salt, 1/4 tsp chilli, 1 tsp LB spice mix (not the plus version ie the std), 1 tsp rajah madras curry powder, 1 tbsp onion paste, big pinch frozen chopped coriander and splash worcester sauce (both added after the base gone in)