After Chinese New Year, the Mid-Autumn Festival is the most important celebration in China. It falls on the 15th day of the eighth month in the Chinese lunar calendar, so the celebration changes each year. This year, the holiday falls on Sept. 24.

Families celebrate the holiday by gathering together to gaze at the moon, according to Time. They also light lanterns. Traditionally the lanterns were paper illuminated by candles, but more recently the lanterns are plastic and inflatable, lit by bulbs inside. Glow sticks have also become part of the modern tradition.

The treat of choice during the Mid-Autumn Festival is the mooncake, a classic pastry that has a salted, baked egg yolk in its center, but there's a lot more to them than just that.

1. Traditional mooncakes contain a paste made from lotus seeds or beans and are sweet.

savory mooncake Some mooncakes are savory, filled with meats or vegetables. (Photo: ZHANGXIAOLI/Shutterstock)

2. There are also savory mooncakes. A popular filling for the savory versions are pork and honey.

3. Pre-made mooncakes are expensive, even though they don't cost a lot to make. Because they are time consuming, are often intricately packaged, and are so traditional that people are willing to spend the money on them, the bakeries that make them charge high prices. Packaging can be as elaborate as a heavy wooden box where each mooncake is individually encased in a round metal container. At Starbucks in China, mooncakes are sold in a three-tiered box with a separate drawer for each flavor, almost like a jewelry or tackle box, reports the Los Angeles Times.

4. You can make mooncakes yourself if you don't want to pay the high price. Although it takes some time, it's not very difficult. Start with an inexpensive mooncake mold that you can find online. The video below takes you step by step through the process.

5. Workers who receive mooncakes as gifts from employers may be taxed for the value of the mooncake in some locations in China, according to China Daily.

6. Mooncakes sometimes enjoy the same reputation as a Christmas fruitcake because they are often unwanted. The Times reports that in 2011, a marketing manager in Beijing had 30 of them piled up on desk at work, all given to her as gifts .

7. In leaner times, mooncakes were high-calorie, sweet, highly anticipated treats. Now that food and treats aren't hard to find, the 800-calorie cakes are considered unhealthy.

mooncakes Modern mooncakes come in various colors with all sorts of fillings. (Photo: Elena Veselova/Shutterstock)

8. The variety of mooncakes has exploded in modern celebrations. They are now made in various colors and flavors with an array of nontraditional fillings. For the past 20 years, Haagen-Dazs has made ice cream mooncakes, sold in China. Oreo also makes a version of mooncake, replacing the lotus paste fillings with flavors such as double chocolate or strawberry jam.

9. In recent years, the mooncake supply has outpaced demand. In 2017, more than 1.5 million mooncakes ended up uneaten and in the trash (along with 40 million glow sticks used during the celebration), according to The Standard.

10. Chinese legend says that mooncakes helped overthrow the Mongolian empire in the 14th century. Expatriate Lifestyle says revolutionaries spread a rumor of a deadly disease that could only be cured with mooncakes. When people cut into their mooncakes, they found a message with the date of the revolt — the 15th day of the eighth month of the year.

Robin Shreeves ( @rshreeves ) focuses on food from a family perspective from her home base in New Jersey.

Everything you need to know about mooncakes (including why they're so expensive)
Mooncakes are a traditional part of the Mid-Autumn Chinese festival. But there's more to the legend of this pricey pastry.