Heat the vegetable oil in a large pan over a medium-low heat. Add the onion and fry for 15-20 minutes until completely soft and golden brown, stirring regularly. (This stage is crucial in creating the base flavour of this dish, so don’t rush it!)
Toast the cumin and coriander seeds in a dry frying pan over a medium heat for a minute or so, until their aromas are released. Grind in a mortar and pestle, then add them to the onion with the garlic, ginger and ground spices. Fry for a few minutes.
Add the chickpeas, tomato, tomato purée, measured hot water,1.5 teaspoons of salt and a generous grind of black pepper. Cover and cook over a medium heat for 45-60 minutes, or until the chickpeas are completely soft and plump. Check on it halfway through cooking and add another cup of hot water if the chickpeas look a bit dry.
Taste to adjust the seasoning, then stir through the cornflour. Cook for a few final minutes for the sauce to thicken, then take off the heat and finish with the extra virgin olive oil.