For the shallots, heat the oil in a large frying pan on a medium flame. Once hot, add the mustard seeds and curry leaves and, when the seeds pop and the leaves crackle, lay in the shallots cut side down and leave to cook for five minutes, until browned.

Now stir the shallots, encouraging the “petals” to break loose, and cook for another five minutes or so, until soft enough to cut with a wooden spoon.

Add the tomatoes, chilli and two tablespoons of water, and cook until the tomatoes go jammy and break down into a paste (you may need to add more water).

Add the tamarind, salt and turmeric, cook for two minutes, then take off the heat and set aside.

In a casserole dish for which you have a lid, heat the oil for the istoo on a medium flame and, once hot, add the curry leaves, cinnamon and onion. Cook for eight to 10 minutes, until the onion is as soft as possible without colouring, then stir in the ginger, garlic and chilli, and cook for two minutes.

Add the potatoes, salt and pepper, stir in the coconut milk, then fill the empty tin with 100ml water, swirl it around and add to the casserole – you want just to cover the potatoes, so add more water, if need be. Bring to a boil on a medium heat, then turn down the heat and simmer for 10 minutes.

Add the beans, cover with the lid and simmer until both the beans and potatoes are tender – around five to six minutes (longer, if you prefer your beans soft).

Gently reheat the shallots, transfer, with the curry, to big bowls, and serve with basmati rice or appams.