Wash the chestnuts thoroughly and peel them.
Steam the peeled chestnuts.
Mash the steamed chestnuts until smooth.
Add sugar and milk to the mashed chestnuts and mix well.
Pour the chestnut mixture into a pan and simmer over medium-low heat, stirring constantly.
When the mixture thickens, turn off the heat and let it cool.
Transfer to a jar and seal tightly.