http://xs128.xs.to/xs128/08255/images_1_329.jpgThis one isnt my favourite dish as both times i've had it they've used too much shatkora (i dont order methi chicken for the same reasons). I would imagine using the standard BIR technique (frying garlic, then onions, tom puree & spices and then meat, base sauce and coriander) and just adding shatkora is how they cook it.
The shatkora looks like a grapefruit but is greeny yellow. You might find them in indian food shops. I found them in brick lane, london along with a couple of other 'new' and ugly citrus fruits. The taste is like a cross between a grapefruit and a lemon but is maybe not quite as nice as either (in me and my housemates opinion). We made citrus variety gin & tonics.
It's got a little bit of bitterness in it too though which isnt so good so i suppose you dont want to use too much.
I found some worthwile tips just now. The below blog from a bangladeshi says you shouldnt be cooking the insides (flesh) of it, which is not how i've had it served to me. There's a recipe there but it's homestyle rather than restaurant. Still, it looks like a good one.
http://dancesylhet.multiply.com/journal/item/2