There is a difference between restaurants (1) OWNED by people from Bangladesh and (2) restaurants SERVING Food OF Bangladesh to NON-Bangladeshis, i.e. anyone who cannot speak Bangla, regardless of skin color!
The # of category (1) is huge and at one time included >80% of all "Indian" joints [emphasis on joints] in the USA & UK. This is where you get the "buffets" with the foods familiar to the US public as "Indian", i.e. type of Restaurant Punjabi much as Restaurant Cantonese became the face of "Chinese" cuisine here.
#2 is vanishingly small! In NYC, around McDonald Ave in Brooklyn, there is a concentration of TRUE BANGLADESHI restaurants that would serve TRUE Bangladeshi Food: fish with bones in that you would need to eat with your hands! Ditto for meat! All of these have thin gravies that need to be mixed with a LOT of rice, NOT SPOONED UP NEAT!!
SAGAR is one of such restaurants. There are many more. You can go to the area & ask, and will be rewarded IF you are willing to jettison your pre-conceived notions of what food should be.
The people who own Kalustyan's are from B'desh. Across the street, is an Indian vegetarian restaurant named PONGAL. The Kalustyan owners had opened a true B'deshi restaurant called SWAGAT right next to PONGAL, in the early 90s. Absolutely authentic, truly excellent home-style B'deshi food, which is EXACTLY the reason it could not survive! Not a single rubbish Indian resto item on the menu!
Edison, NJ is the heart of the Indian ghetto & eateries abound!! The best place to find Indian food! Some examples follow, by no means an exhaustive list.
Bengali Sweets, Jalaram, Chowpatty & Jassi are 4 names that stand out for Indian sweets & savory snacks including the composed items called "chaats". These are to be eaten quickly on site, and the rest can be carried home.
Good reports about SWAGATH at Sugartree Plaza; this is a South Indian vegetarian place without a buffet. Ditto SAPTHGIRI. HOYSALA serves the food of Karnataka.
SIGIRI is a branch of the Manhattan Sri Lankan restaurant, in Edison, reputed for good food. No buffet, but prices very reasonable.