Soak the chestnuts in very hot water for 10 to 15 minutes. Peel off the outer shell and inner skin with a knife. If the inner skin is hard to peel, return the chestnut to the hot water again.
If you soak the chestnuts for a while, the inner skin will soften and become easier to peel. The peeling is the most difficult part, but keep at it! You'll be rewarded with the delicious chestnuts you'll get in the end!
When all the chestnuts have been cleanly peeled, soak them in water for half a day to get rid of the bitterness. You can just soak them for a few hours, but I think they come out nicer if you soak them for half a day.
Put the chestnuts and plenty of water in a pot and start heating. When it comes to a boil, cover with a small lid that sits right on top of the contents of the pan (a drop lid or otoshibuta; you can substitute this with a piece of aluminium foil) and simmer over very low heat for 15 minutes.
Put the pot in the sink and run water into to cool the chestnuts. When the water in the pot is cold, fill with fresh water and heat again.
When it comes to a boil, simmer over very low heat for another 15 minutes. You should be able to break apart the chestnuts with your hands, and they should still be a bit hard when bitten into.
Cool the chestnuts down again under running water as in Step 5, and soak in the cold water until they are completely cool.
Next, put water and the first 100 g batch of sugar in the pan and heat.
When the sugar starts to dissolve, put the chestnuts in gently. When it starts to boil, turn off the heat. Leave as-is overnight.
The next day, add another 100 g of sugar and heat until it starts to boil. Turn off the heat, cover with a drop lid, and leave to cool down and rest for half a day.
Put the last 100 g batch of sugar in the pan and bring to a boil again, then turn off the heat. Cover with a drop lid again and leave to cool. When it has cooled down completely, place only the chestnuts (not the syrup) into jars.
Heat the syrup again, bring to a boil, skim off any scum, and pour into the jars over the chestnuts. When the syrup cools, it's done!
Any chestnuts that couldn't be immersed in syrup can be frozen.
Here's an example of a schedule for making the chestnuts in syrup: Peel the chestnuts in the morning, and leave to soak for half a day to rid of bitterness. Boil twice, adding the first batch of sugar for the initial simmering. Leave to rest overnight.
The next morning, add the second batch of sugar, simmer and rest until the evening. Add the last batch of sugar in the evening. Put the chestnuts in jars later that night. This way you can do all 3 sugar additions in 2 days.
If you remove crumbled chestnuts as you go, the syrup won't become cloudy. Cut off any discolored bits too, if you notice them.
Story Behind this Recipe
My whole family loves simmered chestnuts in syrup, and I wanted to eat a bunch of them to my heart's content - so I made my own. I referred to an old fashioned, slow-cooking method, and cut a few corners while still ensuring that they came out nicely. If you take your time to make these, they say you should end up with lovely glossy-looking chestnuts!
One of the keys to a nice finish is to thoroughly get rid of bitterness. I tried shortening the soaking step once, and the chestnuts came out looking rather dark. When cooling the boiled chestnuts, if you don't soak them in water until they have completely cooled, their surfaces will become dry and flaky. Chestnuts can fall apart easily, so handle them gently.