Soak tamarind in water for at least 30 minutes and take thick juice.
In heat little oil, add split bengal gram, coriander seeds, dry chili and roast them until they turn golden brown. Cool this to room temperature and grind this along with coconut pieces into a fine thick paste by adding little water as possible. Add this to cooked (mashed) pigeon pea and mix well.
In a pan heat oil as needed. add cut bitter gourd and sauté them.
Now add tamarind juice, chili powder mix well and cook until the raw smell is gone.
Now add the pigeon pea mixture, jaggery and continue cooking.
In a separate pan heat oil. add mustard seeds, split black gram, curry leaves. once the mustard seeds stop splattering add this to cooking kuzhambu and mix.
Cook the kuzhambu until right thinness reached and serve.