Soak the chickpeas in plenty of cold water overnight. Check them after several hours to make sure that they remain covered with water as they swell.
Drain the chickpeas and put them in the food processor. Add the onion, garlic and fresh herbs. Whizz them to a manageable consistency, a mass that sticks to itself, but is not yet mushy or pasty. You will need to stop the food processor and scrape the sides down a few times.
Add the spices, flour, baking powder and salt. Add 3 tablespoons of water. Run the food processor again to blend. Add the final tablespoon of water if it seems necessary to hold the mass together.
Turn the chickpea mass out into a bowl for convenience. Heat the oil in a heavy pan until it shimmers.
Wet your hands and form a round ball about the size of a walnut in its shell. It might be a little loose; don't be afraid to compact it. Fry this first falafel ball. Taste it and adjust seasoning in the raw mass if needed. Don't be tempted to make bigger balls with an ice cream scoop or otherwise: the outside will cook before the inside is edible. You may place the balls on top of a small plateful of sesame seeds before deep-frying; the seeds will stick to the bottoms decoratively.
Fry until the outside of the falafel balls are brown and crisp, and the inside is cooked through. The first experimental ball will tell you how long to keep them in the oil, although as you proceed, they will fry more quickly. Don't crowd the falafel balls while frying. When they are ready to remove from the oil, drain them on crumpled paper and serve right away.