Freelance mathematical sculptor and designer George W. Hart likes to play with his food. Just take a look at his "Mobius" bagel, a play on the eponymous scientific concept of a surface with only one side and only one boundary component.
The bagel itself isn't actually a Mobius strip. It's rather made with two strips, which are the cutting surfaces; one for each half. Hart's website has detailed instructions for how to make your own, as well as other foodie-math projects. He also teaches how to turn a bagel into a trefoil knot (that's when two loose ends of a common overhand knot are joined), how to make cookies that look like trilobites (a fossil group of extinct marine arthropods) and the mathematics behind impossible food combinations.
In an interview with HuffPost, Hart described the simit, a popular Turkish bread baked in a circle and covered in sesame seeds. He first learned about it from Nathan Myhrvold, Microsoft's former chief technology officer.
For your geek food readers, I should also mention that when I showed Nathan Myhrvold the linked bagel cut, he told me about simit, which I hadn't encountered before. I found a simit bakery in NY, and as Nathan predicted, it is great for doing the linked cut.
Click through the below gallery and video for Hart's step-by-step guides to making your own "Mobius"-esque bagel.
How to Slice a Bagel into Two Linked Halves
To start, you must visualize four key points. Center the bagel at the origin, circling the Z axis. A is the highest point above the +X axis. B is where the +Y axis enters the bagel. C is the lowest point below the -X axis. D is where the -Y axis exits the bagel.
These sharpie markings on the bagel are just to help visualize the geometry and the points. You don't need to actually write on the bagel to cut it properly.
The line ABCDA, which goes smoothly through all four key points, is the cut line. As it goes 360 degrees around the Z axis, it also goes 360 degrees around the bagel.
The red line is like the black line but is rotated 180 degrees (around Z or through the hole). An ideal knife could enter on the black line and come out exactly opposite, on the red line. But in practice, it is easier to cut in halfway on both the black line and the red line. The cutting surface is a two-twist Mobius strip; it has two sides, one for each half.
After being cut, the two halves can be moved but are still linked together, each passing through the hole of the other. (So when you buy your bagels, pick ones with the biggest holes.)
Eating a bagel this way has its benefits: It fits more cream cheese because there is slightly more surface area.
Using a Simit
An animated Gif of the same process using the round Turkish bread.