Rinse and peel the taro root potatoes. The root potatoes are slippery when wet, so either drain well or blot off excess water.
Since the root potatoes get slippery when peeling, it's best to hold them at the top and bottom, and peel lengthwise, then peel the ends last.
After rinsing the root potatoes again, drain, then rub in salt (for boiling) to remove the starchiness.
Add to boiling water as is, and boil for 4 to 5 minutes, remove scum that rises to the top, then rinse.
Put the sauce and root potatoes in a pot, cover with a drop lid, and bring to a boil on high heat. Reduce to low to medium heat after boiling, then simmer (for about 10 to 20 minutes).
Once they are tender enough to pierce with a toothpick, remove the lid, and heat on high flame until the sauce is reduced.
Story Behind this Recipe
I have been preparing taro root like this for a long time.
If not serving right away, remove from heat while still on the raw side, allowing them to cook with the residual heat, then simmer again right before serving. This will come out light tasting, so adjust the seasoning to suit your taste. I personally like the balance of 2 parts sugar to 1 and 1/2 parts soy sauce.