Photo: Ria Osborne
Cut the sweet potato into 2cm cubes. Put the sweet potato, lentils and stock in a large pan, bring to the boil. Simmer for 20 minutes, stirring occasionally.
Meanwhile, toast the spices in a dry frying pan for 2 minutes, transfer three quarters to a pestle and mortar and grind to a powder, transfer the rest to a bowl. Set aside. Add the oil to the frying pan; add the onion. Cook for 15 minutes until soft, then stir in the garlic, ginger, chilli and ground spices.
Stir the spiced onions into the lentils and, over a low heat, add the spinach a handful at a time, stirring until wilted; season.
Serve the dhal in bowls, with a dollop of yogurt, coriander and mango chutney. Sprinkle over the reserved spices and chilli.