Make the filling a day before you want to make the tang yuan.
In a dry frying pan, add the peanuts and toast over medium heat, for 3-5 minutes, until aromatic.
Remove peanuts and let cool.
Add the cooled peanuts to a spice grinder or food processor and blitz together with the granulated sugar, until you obtain a coarse powder. (Be careful not to over blitz or it will turn into peanut butter).
Dump the peanuts into a small mixing bowl. Add the peanut butter, icing sugar, and coconut oil and mix together until you obtain a firm consistency (not too runny, and not too stiff). If it's too runny, add a little more icing sugar. If too stiff, add a touch more coconut oil. It will firm up in the fridge.
Cover the bowl with plastic wrap and place into the fridge to stiffen.
When ready to make the tang yuan, remove the peanut filling from the fridge and use a melon baller to scoop small portions. Use the warmth from your hands to help mold the shape of the peanut filling.
Place the formed peanut filling balls onto a plate lined with plastic wrap.
Keep in the fridge until ready to use.