Doughnuts are a sweet treat made from a mixture of flour, granulated sugar, butter, and eggs, then fried in oil.

The most common shapes for doughnuts are either a hollow ring or a closed type with fillings such as cream or custard injected into the dough.

Apart from the traditional doughnuts, there are numerous other variations available, including fruit-flavored, cheese-filled, chocolate, and more. Different regions also have their unique flavors and methods of making doughnuts, such as the "beignet" in New Orleans and the "doughnut muffin" in Texas.

<b>The Making Mystery</b>

Eugenia Cheng, a mathematics lecturer at the University of Sheffield in the UK, uncovered the secret to delicious doughnuts using calculus formulas. Through her calculations, she determined that the diameter of a doughnut should be between 72mm and 82mm, with the optimal diameter for the central hole being 11mm.

This way, the "soft-crisp ratio" of the doughnut can reach the golden ratio of 3.5 to 1. For those who prefer a softer texture, a smaller hole can be made, while those who enjoy a crispier crust can opt for a larger hole. She also calculated the ideal amount of glaze to coat a doughnut: 5.8 grams. However, she admitted, "These calculus formulas can easily make your head spin. It's better to just eat them however you like."

<b>History and Culture</b>

Doughnuts originated in the Netherlands and were brought to the United States in the 16th century. The original doughnuts did not have a hole. It wasn't until 1847 that a sailor named Hanson Gregory invented the distinctive shape, making it easier to bake and flip them on ships.

In 1921, Adolph Levitt, an American, invented the automated doughnut machine, which, paired with pre-made batter, could produce 960 doughnuts in an hour, significantly reducing production costs and leading to the prosperity of the doughnut industry. In 1919, doughnut sales in the United States amounted to $5 million annually, but by 1935, sales had skyrocketed to $33 million.

During the 1930s, doughnuts became a staple food for many due to their affordability. At that time, thoughtful shopkeepers would often include a note with doughnuts: "As you go through life make this your goal: Watch the doughnut, not the hole." Just as optimists see a glass half full while pessimists see it as half empty.

In Asia, doughnuts are primarily considered snacks, but in the United States, many people have doughnuts as a staple breakfast food, and there is even a "National Doughnut Day" celebrated.

Today, doughnut shops can be found in every corner of the world, and bakers from various countries continue to innovate and improve doughnuts in various styles. Whether upscale or casual, traditional or trendy, doughnuts are a food that appeals to everyone.

However, it's also important to be mindful of the calories and nutritional value of doughnuts and consume them in moderation to fully enjoy the deliciousness and joy they have.