Heat the oil in a large pan with a lid – you’ll need the lid later – over a medium heat.
Add the mustard seeds and cumin seeds. Fry for 30 seconds or so until the seeds are starting to pop.
Add the onion, garlic, dried chillies and curry leaves. Cook slowly, stirring regularly, for about 10 minutes or until the onions darken in colour.
Add the turmeric and tomatoes. Stir over the heat.
Add the black beans and the tomato puree.
Add 350ml of water or stock, just enough to reach the top of the beans.
Bring to the boil then turn down to a simmer and leave to cook for 15 minutes, stirring occasionally to stop the bottom from catching. The liquid should reduce to a thick gravy.
Mash the beans with a potato masher but leave some intact. If your curry seems very thick, add another 50ml or so of hot water.
Add the shredded spinach and stir through.
Stir in the fresh chopped chilli and a pinch of salt and pepper to taste (if your beans were preserved in brine, you won’t need much salt).
Sprinkle with fresh coriander and serve.
Video
Notes
Some brands of canned black beans are darker in hue than others. This can depend on a variety of factors, including when they are harvested and how they are processed. In any case, whether pitch black or more reddish in hue, they should taste delicious in this curry.