First you need to make a curry paste.
Toast the cardamon pods and all seeds in a dry pan until they smell great
Add with the cloves to a mortar and pound discarding the cardamon shells leaving only the seeds, until a powder is formed.
Add spices, red chillies, 1tsp salt, tomato puree, white wine vinegar and 2 tbsp olive oil and make into a paste.
Heat remaining oil in a pan and cook the onions until nice and soft.
Add the paste you have already made and fry for about 3 minutes. This will smell amazing!
Add 450ml water, tomatoes, sugar and the remaining salt and simmer for about 15 minutes.
Add the potatoes and cover with a bit more water if necessary.
Cover and cook gently for 20 minutes.
Check the potatoes are tender, there is nothing worse than an undercooked potato in your curry!
Check seasoning.
Add the spinach until just wilted.
Stir through to combine and serve with chopped coriander and chapatis or rice.