Here's a base that I've now had my best results from. I'll post the final curry recipe later. This base has some of the originality of the KD base but the beauty of it is you don't get the boiled onion smell/taste as this base has so much oil (that can be reclaimed). A restaurant owner told me this was the way he did it. It makes sense to keep it all in one pot if you're running a BIR.
12 onions (2kgs), roughly chopped
1 green pepper, chopped
600 ml veg oil
water, enough to just cover the onions in the pan
1 tbl salt
1 big bulb of garlic, chopped
1 hpd tbl ginger paste
2 tbl tomato puree
1 tin tomatoes
2 tbl coconut cream
1 tsp ground cumin
1 tbl ground coriander
1 tbl turmeric
1 lvl tsp garamasala (I use Natco)
1 cinnamon stick (2 inches)
1. add everything except the spices to the pan and bring to the boil
2 once boiling added the cumin, coriander, turmeric, garamasala, cinnamon stick and cook for 80 mins, lid on stir occasionally
3 discard cinnamon stick, cool down mixture (I put pot into a sink filled with water to rapid cool). I think this cooling is important to the final taste.
4 blend using a strong hand blender until the mixture is completely smooth. Add water to get a very runny soup type consistency
5 bring to boil and skim off the frothy scum that floats to the top for 15 mins.
6. once the mixture looks 'clean' boil on medium until the oil separates and collects at the top. Should get a nice thick layer of deep red oil floating at the top.