emin-j,
best of luck for Saturday.
the onion is for defo critical along with it's cooking stage. i think u would need a proper "chopper" to cut the onion fine enough but maintain a consistent shape. i've tried grating and that does not work (
https://curry-recipes.co.uk/curry/index.php?topic=3393.10). i have made onion paste (which is kind of similar) in 2 ways: blend onion 1st or at the end. trouble is i can't see blended working either.
i've no real experience of traditional cooking which did not help. it did take me back to pre KD1 days when i used to make curry from scratch using butter, onion, chopped tomato and a made up spice mix from a lady on wolverhampton market.
on your go i'd be wary of the ginger. in the 1st go following the restaurant method it did not cook out and i chopped very fine. on the 2nd go there was just too much of it.
i might also reduce the tom puree slightly to say 1/2 tsp as in this sort of curry u want it subtle. if u're adding cream (which i didn't as i made madras) u won't notice the need for it.
best wishes,