Wrap the sweet potatoes with aluminium foil tightly.
Arrange the aluminium foil wrapped sweet potatoes on a frying pan or a skillet over low heat.
Place a lid over the frying pan or the skillet and roast the sweet potato slowly for about 1 hour. *2
Turning the sweet potatoes about 90 degrees every 15 minutes.
Insert a skewer, if the sweet potatoes are soft, turn the heat off and serve.
*1 see the information in the post how to choose good sweet purple potato, 6-8cm (2.5-3inch) in diameter is ideal size. *2 depends of the size of the sweet potato, you may need to adjust the cooking time less or more.