My earlier comments on a different NYT butter chicken recipe are on the NYT thread linked below.
This one uses only ground garam masala, no cumin or coriander or whole spices, so it makes sense it tasted flat. Suggest adding those as well as the kasuri methi I linked in the other thread.
Coconut milk does not go in butter chicken – finish with heavy cream or sour cream or creme fraiche. Or pureed cashews if you don’t want any of the the creams.
