Hello fellow curry lovers

I need help... I'm a curry fiend with a problem!
I've been trying and trying to replicate my local curry house balti sauce but with no success. It just lacks that depth of taste i can't seem to achieve. Its the sauce of choice because it suits all tastes and i've roped myself into doing a curry night next week for 7 friends and myself, and ive been practising all week but i'm not 100% happy with the sauce.

This is the recipe i've been following :-

Ghee
3 large onions
400g chopped tinned tomatoes
1 tbsp garlic and ginger paste
1 tbsp paprika
1/2 tsp ground turmeric
1/2 tsp ground cumin
1/2 tsp ground coriander
1/4 tsp chilli powder
1/4 tsp ground cardamom
1 bay leaf
Salt and pepper

It just tastes bland, no depth of taste and the spices taste raw, even tho i cook them out for longer than the required time.

Any advice would be greatly appreciated

Cheers.