Mix all the ingredients in a small bowl fitted on top of a saucepan with boiling water (i.e. double boiler). Do not let the boiling water touch the bottom of the bowl.
Heat over low heat. Stir the mixture constantly with a spatula until it becomes solid and doesn't stick to the spatula anymore. Cool and refrigerate for 2 hours.
Makes approximately 8 ounces and is sufficient for 9 snow skin mooncakes.