To make the curry ice cubes, peel the garlic cloves and onions, half the tomatoes and remove the stem. Add them to the bowl of a food processor along with the ginger (no need to peel, just wash well), tomato purée and salt (if you have coriander flying about, you can also add the stems to the processor) and blend into a purée. Heat the oil in a casserole (the wider & shallower, the quicker the process) and carefully tip in the mixture. Bring it to a boil, then cook over medium heat until most of the water has evaporated and it has thickened into a paste (30 - 60 min). It will splash quite heavily while it cooks, so keep it loosely covered with a lid but allow the steam to escape.
In the meantime, toast the cumin and coriander seeds in a frying pan until aromatic. Then use a spice grinder or pestle & mortar to crush them into a fine powder. Tip it into a small mixing bowl and combine with the garam masala, turmeric and chilli powder.
When the aromatics have reduced to a paste, stir in the spice blend and let them cook for 30 seconds, then turn off the heat. Set the pan aside and let the paste cool entirely, before dividing it over giant ice cube trays and using it whenever you fancy a curry.
To make the Chickpea & Spinach Curry, simply heat 3 giant curry ice cubes together with the coconut milk in a casserole until completely melted. If using dried soaked chickpeas, drain them and cook them in plenty of water for 1 1/2 hours or until tender. Drain the tinned or cooked chickpeas and add them to the pan along with the spinach. Cook until the spinach has wilted and the curry has thickened. In the meantime, roughly chop the coriander and set aside. When the spinach is ready, stir in the juice of half a lemon, then serve with rice, the chopped coriander and an extra squeeze of lemon juice.