Sweet potato leaves ('mtoriro') are one of the foods that you find sometimes when you live in Zanzibar, but don't tend to come across as a tourist much. But these young leaves are really tasty and nutritious and can be used instead of spinach ('mchicha'). Ask around for them if you are in Darajani market near Stone Town - small bundles of arrow shaped green leaves you buy in bunches and which are wrapped up in newspaper for you to take home.
When you get them home, strip of the bigger rougher stems, wash the leaves and then put them out in the sun for a couple of hours to dry out.
When you are ready to cook them, first of all boil a pan of water. Put in the leaves and boil them for no more than 5 minutes until soft. Then drain the water off, add fresh coconut milk (or tinned if you don't have access to fresh), some chopped onions, garlic, ginger and some fresh lime. Cook on a low heat until the sauce has reduced a bit but not so long that the coconut milk gets slimy. The leaves remain dark green and have a little bite to them still, with a dense, ever-so-slightly bitter flavour offset by the creamy coconut.
Serve with fish and rice for a healthy Zanzibari meal. Here it's pictured with swordfish in vegetable sauce and local rice. For a twist on the recipe you can cook sweet potato leaves with chopped unripe mango.