Add the chickpeas to a small pot with their liquid and enough water to keep them covered.
Add the tea bags, bring everything to a boil, then turn the heat down as low as possible and simmer gently for 20 minutes.
Heat the oil in a kadai or deep frying pan.
Add the cumin seeds, cinnamon stick, cassia leaf and black cardamom.
Fry for a few seconds until fragrant, then add the grated ginger and cook briefly.
Add the finely chopped onion and green chilli.
Turn the heat down and cook gently until the onion is completely soft and golden.
Pour in the puréed tomatoes, followed by the turmeric, chilli powder and ground coriander.
Mix well and leave the masala to cook down.
Stir regularly until it has thickened into a paste and you can see the oil beginning to separate around the edges.
Season with salt.
Remove the tea bags from the chickpeas.
Add the chickpeas to the masala a little at a time, along with some of their cooking liquid.
Stir everything together and leave it to bubble gently for a few minutes so the chickpeas absorb the flavour.
Add more cooking liquid if you prefer a looser gravy.
Finish with the amchoor powder, which adds a sharp, slightly fruity sourness, and plenty of chopped coriander.
Serve hot with basmati rice.
