Wash bitter gourds and remove scaly skin with a potato peeler, then rub with a little salt and brown sugar. Put aside for 1 hour.

Heat oil in a pan.

Add chopped onions and all spices (red chili powder, turmeric powder, coriander seed, fennel seed, nigella seeds), except the tamarind juice, to the heated oil.

Sauté the onion and spice mixture, ensuring not to burn the onions.

Once the onions are tender, remove the mixture from the oil and drain it well.

Allow the sautéed onion mixture to cool down.

Rub off the excess salt and sugar mixture from the bitter gourds, or wash them off and pat dry with paper towels.

Make a lengthwise slit down each bitter gourd, remove the seeds and stuffing pulp, but don't discard the pulp.

Stuff each bitter gourd with half of the cooled onion mixture. Add a small amount of the reserved seed pulp (add very little if you don't like a very bitter taste) and a little tamarind juice inside each bitter gourd.

Bind each stuffed bitter gourd by wrapping it with thread to prevent the stuffing from escaping.

Fry the wrapped karela in oil until golden brown on all sides.

In a separate pan, add the remaining onion mixture, tamarind juice, and a little oil.

Place the fried stuffed bitter gourds in the pan with the onion mixture and tamarind juice.

Cover the pan and simmer for 10 minutes, allowing the flavors to meld.

Serve hot.