Peel and cut yam into small pieces
Start by steaming your cubed yam over high heat until it is fork-tender (usually 30 - 45 minutes). It is crucial to steam it thoroughly so you don't end up with lumps in your paste.
Remove yam from steamer while it is still hot and mash thoroughly with potato masher or a fork. Add sugar, water and about ⅔ of the oil and mix well. Mash yam with a fork until fine.
Pour the remainder oil into a non-stick pan and transfer the puree to the pan. Add the sugar and oil in stages. Cook over low to medium heat, stirring constantly. You are looking for the paste to leave the sides of the pan and form a firm, non-sticky ball. This can take 30–45 minutes of patience!
Once the paste has reached the desired firmness and has a matte finish, fold in your toasted peeled melon seeds. These provide the essential "crunch" that defines a traditional yam mooncake.
Allow the paste to cool completely before using it for your mooncakes. You can store this in an airtight container in the fridge for up to a week.