This is a cheap and easy dish. You could add chopped cauliflower, red pepper or aubergine before the sweet potato; throw in shredded cooked chicken with the tomatoes; add raw prawns or white fish pieces 5 minutes before the end of the cooking time; or serve in a flatbread with grated carrot, coriander and shredded lettuce

Heat the olive oil in a large saucepan over a medium heat. Add the onion and curry paste, mix well, then cook for 10 minutes, stirring occasionally, until the onion is soft and golden.

Add the chilli, ginger, coriander stalks, sweet potato and chickpeas. Cook for 5 minutes.

Add the tomatoes and 200ml water and bring to the boil. Reduce the heat to a simmer, then cover and cook for 10?15 minutes. Remove the lid, then cook for a further 15?20 minutes, stirring occasionally, until the sweet potato is cooked through and the sauce thickened.

Stir in the coconut milk and cook for a couple of minutes, then stir in the spinach and cook until wilted. Serve with poppadums and rice.

To freeze the curry for another time, leave to cool in the pan, then spoon into portion-sized containers or freezer bags and freeze. The curry will keep there for up to 3 months.