I made these last year, a little too late for mooncake festival as I didn't get my mooncake moulds until later. The process can be pretty involved if you choose to make everything from scratch, such as the sugar syrup and fillings. If you wish to buy premade syrup and filling, the process will be a lot faster, however, I think that it's probably worth making your own if you're going to go through the prcoess of making these in the first place, since the taste will be a lot better.
I got the recipe from Jo at http://www.jodelibakery.netfirms.com/ and it is a success! I had to make my own syrup since I could not find any. The recipe below is for the syrup solution.
600 g sugar
500 g water
A few lemon slices
2 Tbsp molasses
Boil the sugar and water on low heat until thick and golden, then add 2 tbsp molasses and 1 tsp vanilla.