Cut the sweet potato into 1 cm slices. Throw these slices into a pot with enough water to cover them.
Add the sugar and lemon, and simmer on medium heat until your sweet potatoes are tender.
Decorative touch for o-bentos.
Make shallow cuts into the skin of the sweet potato slices (just deep enough to pierce through the visible section).
Continue to peel the rest of the slice, but skip over every other section of skin, so as to create an alternating striped pattern.
Story Behind this Recipe
I posted this recipe here in response to a request from a follower on my blog.
Adjust the amount of sugar to taste. For those who dislike tartness, add a little bit of mentsuyu noodle dipping sauce (although the color of the potato might become less vivid). When packing them side by side in your obento, alternate the alignment of the skin to create a checkered pattern.