Bring a pan of salted water to a boil, add the spinach and blanch for a minute.
Drain in a colander and run under cold water to stop the spinach cooking anymore. With the spinach still in the colander, using a large spoon or potato masher to squeeze out any excess liquid. Lay the leaves on a chopping board and chop, then set aside.
Heat the oil in a large frying pan. Add the asafoetida, mustard and nigella seeds, when the seeds begin to pop add the onion, garlic and chilli.
After around 4 mins, tip in the diced potatoes, season with salt and cayenne pepper, fry for a couple of mins.
Add 5-7 tablespoons of water, cover and gently cook over a very low heat for 20mins, until the potatoes are tender, stirring the pan every so often, ensuring the potatoes don't stick to the bottom of the pan.
After 15mins, add the tomatoes, stir and cover.
Add the blanched spinach, the the mixture a stir and cook for 1-2 mins until the spinach is heated through.
Serve immediately
