Fry white sasame seeds in a pan without oil until fragrant comes out.
Wash sweet potatoes, remove skin and cut into smaller chunks. Fry in heated oil until golden brown, and drain oil and reserve for later use.
Heat oil in wok, andd in rock sugar and water and stir continuously until sugar melts.
When sugar darkens slightly and thickens, stir in sweet potatoes and stir until well combined and place on serving dish. Garnish with sasame seeds.