In a mixing bowl, whisk together all the ingredients until well combined. Pour the mixture into a deep plate or shallow bowl.
Steam over medium heat for 15 minutes. (If the ingredients are doubled, steam for an additional 5 minutes.)
Scrape the hardened dough off the plate onto a work surface. When cool enough to handle, knead until smooth and elastic. (Gloves will help prevent sticking and are highly recommended.)
Wrap in plastic wrap and refrigerate for 2 hours.
Color Options:
If you wish to color the dough, add the color during kneading and continue kneading until it is well distributed. Add color little by little until the desired color appears.
Custard paste (with variations including chocolate), red bean paste, lotus seed paste, sesame seed paste, or anything that you can reasonably shape into a ball.
Assemble the Mooncakes:
Divide the dough into 9 equal pieces and shape into balls. Form 9 equal balls of filling.
Flatten each piece of dough into a round wrapper with your fingers. Place filling in the center of the wrapper and seal.
Insert ball (seam-side facing you) into a 50 to 75 gram mooncake mold dusted with powdered sugar to prevent sticking. Invert the mold onto your work surface and push gently to press into shape.
Place onto a wax or parchment paper lined tray. Makes 9 mooncakes.
Serving & Storage:
Mooncakes may be served straight away after assembling.
Otherwise, place them in a single layer in an air-tight container and refrigerate up to 48 hours. Remove from the refrigerator 1 hour before serving.
Mooncakes can also be frozen in an airtight container for up to 1 month. Thaw in the refrigerator before serving.