A rich thick filling usually made from red bean or lotus seed paste is surrounded by a thin, 2–3 mm (approximately 1/8th of an inch) crust and may contain yolks from salted duck eggs. Mooncakes are usually eaten in small wedges accompanied by tea.
Sour Cream or Yogurt Or, if you want to make it even moister, you can proceed with your recipe for 12 cupcakes as is and add 1/2 cup of sour cream or yogurt instead. This acidic dairy product adds moisture to cupcakes and makes it denser as well.
According to various Internet sources, including these by Mental_Floss and io9, velvet cakes of the past were made with baking soda and either vinegar or buttermilk. When the baking soda combined with either of these two ingredients, it would bubble up and cause the cake to have a fluffy and smooth texture.