To Prep
Peel the sweet potatoes, chop into small chunks and soak it in a bowl of water for 2-3 hrs.
To Cook
Boil it in a pot of water until it becomes soft.
While the sweet potato is still soft, strain it through a sifter to make it into a puree.
Mix the sugar, syrup and mirin in a saucepan and cook over low heat until it starts to simmer.
Turn the heat off, add pureed sweet potato and mix them well together.
After mixing it well, cook over low heat for 15 mins. Keep stirring to avoid mixture from sticking to the bottom.
Turn off the heat, add the chestnuts and cover them with the pureed sweet potato mixture. Serve cool.