Peel the sweet potato and cut in to chunks of about 1 inch thick
Peel and finely chop an onion
Deseed and finely chop 2 green chillies (Tip: If you want to make the dish less spicy put a small slit in each of the chillies and use them whole, fishing them out at the end)
Roughly chop 2 medium tomatoes
Combine the turmeric, ground coriander and ground cumin
Combine a small amount of tamarind concentrate (just the tip of a teaspoon) with boiling water. You don't want to overdo tamarind as it has a very distinctive taste! You can leave this out if you don't have any.
Heat the ghee or oil in a non stick frying pan and add the mustard seeds.
When the popping of the mustard seeds slows add the onion and green chilli and fry gently for about 5-7 minutes until the onion is soft
Add the garlic and ginger pastes and fry for 1 minute.
Add the turmeric, coriander and cumin mix and fry for 30 seconds before adding the chopped tomatoes. Season with salt and black pepper and fry for about 1 minute.
Add the coconut milk, the sweet potato chunks and the drained chick peas, stir, cover and simmer for around 15 minutes until the sweet potato is soft enough to pierce easily with a sharp knife.
Add the spinach, garam masala and some of the water from the tamarind and cook until the spinach has wilted.