Cut sweet potatoes into big pieces. (Not too thin) (I cook when I am cooking turkey) Put 5g butter on each end. Spread sugar close to the butter so that the butter can melt the sugar. Spread some water on top of potatoes.

Set the oven at 375 degree. Every 30 minutes, take out to mix the butter sugar with sweet potatoes and spread water again. Cook until the sweet potatoes soft.