1. Heat the coconut oil in a deep saucepan and fry the onions over a medium heat with a pinch of salt for 5 minutes, stirring regularly until they start to soften . Add the chillies and cook for another couple of minutes until everything in the pan is soft and fragrant. Add the cumin, coriander and mustard seeds and when the mustard seeds start to pop, stir in the ground turmeric and cardamom.
2. Quickly add the lentils, coconut milk and stock to the pan. Bring the dhal to the boil, then turn the heat down to a gentle simmer. Cook for 25-30 minutes until the lentils have softened and are cooked through.
3. Now make your herb and cashew topping. Roughly chop the cashews and green chilli as well as the whole lemon half, discarding any pips, then add the coriander and chop the lot together with a good pinch of salt to make a rough lemon salsa .
4. Back to the dhal: stir through the spinach and the chopped tomatoes so the spinach wilts a litt le, then taste it and add the juice of up to 2 lemons, depending on your preference . Add salt and pepper to t aste .
5. If you are using the curry leaves, melt about a teaspoon of coconut oil in a frying pan and when the surface is shimmering, fry the leaves for about 15 seconds to crisp up.
6. Spoon the dhal into bowls, top with the curry leaves and cashews and serve with rice or warm roti breads.