Cut the sweet potatoes including the skin diagonally into 1 cm slices, or cut into thin round slices. Next cut them into 1 cm pieces (as seen in the photo), then soak in water to remove the bitterness.
Soak for about 10 minutes. Strain the water but leave the potatoes slightly damp. Transfer to a plate, cover with plastic wrap, and microwave for about 3 minutes at 500 W.
Heat a pan, melt the butter, then fry the sweet potatoes with salt and pepper.
Finally, coat with the sugar, fry some more, and you're done.