Chop onions and garlic very finely and fry in a saucepan with oil for 5 minutes over medium heat, stirring occasionally.
Then add the mustard seeds, cumin, turmeric, chilli, corina seeds and cardamom and fry.
Wash the lentils well and then add them to the pot.
Deglaze with coconut milk and stock and stir. Add kaffier leaves and simmer gently for 30 minutes with the lid closed until the lentils are soft. Possibly add a little more stock or coconut milk.
Cut the tomatoes into wedges and add to the dahl with the spinach.
Season to taste with salt, pepper and lemon zest.
Divide the dahl into bowls and serve with yogurt, cashew nuts and herbs.