Put the yogurt in a large bowl. Beat lightly with a fork and whisk until creamy and smooth. Slowly add 5 cups water and mix.
Put the chickpea flour in another large bowl. Very slowly, add the yogurt mixture, mixing well as you do.
Remove lumps as they appear, and strain it if the final paste is still lumpy.
Heat the oil in a large pan over medium heat. When hot, add the cumin seeds, fennel seeds, nigella seeds, fenugreek seeds, and last of all the red chillies. When the chillies darken, add the coriander and turmeric, and a moment later, the chickpea flour and yogurt mixture.
Add the salt and bring to a boil. Turn heat to low, cover partially and simmer for 25 minutes. Turn off the heat.
While that is cooking, make the dumplings.
Put the chickpea flour in a bowl. Add the salt and baking soda.
Mix. Add the yogurt and mix well with a wooden spoon. You should have a thick but "droppable" paste. Add more yogurt if necessary.
Continue to beat the paste vigorously with the wooden spoon for about 10 minutes, or until it becomes light and airy.
Put vegetable oil into a large frying pan to about 3/4 inch deep. Heat the oil over medium heat.
When oil is hot, lift up a blob of paste, about 3/4 inch in diameter, on the tip of a teaspoon. Release it into the oil with the help of a second teaspoon.
Make all the dumplings this way, dropping them into the oil in quick succession. Turn the dumplings around and fry them slowly until they are cooked through and reddish.
Remove the dumplings with a slotted spoon and pace them on a plate lined with absorbent paper towels. Let them cool slightly and then cover tightly.
10 minutes before you eat, heat the soup mixture over medium heat.
When hot, add all the dumplings, then cover and simmer for another 10 minutes.