Traditionally, kochu shaak is cooked with Ilish macher matha or Hilsa fish head, but another variant of Kochu shaak preparation that is popular among Bengalis is kochu shaak cooked with shrimps. In my maternal home, everyone is gaga for kochu shaak. Though ours was not a traditional joint family, but all the brothers of my father lived next to each other in the same plot. As a result, we grew up as a very close-knit family. Whenever there was something exotic cooked at anyone's home, my aunts or my mother would make sure to share it among each other. Kochu shaak was one such decadence everyone would like to celebrate. Of all the kochu shaak preparations, my mother's one I liked best. She made this dish so tasty that I could eat one plate full of rice only with this dish by my side. It tastes nice with roti too, but I think it tastes its best when accompanied with rice.
Kochu shaak is not available in all the Indian grocery stores here, especially, in the part of USA we are staying now. We searched in every nook and cranny before laying our hands on kochu shaak, some 60 miles away from our place, and so naturally the joy was beyond description. I tried to emulate my mother's version of kochu shaak dish, and it came out really nice. My husband was totally drooling over it.
However, before you go ahead with this preparation, remember to have plenty of time in your hand because this dish calls for an hour or more time of devotion to bring the richness.