We've all seen those holiday cookies with pictures inside. You buy a roll of dough, slice the cookies, and bake. Kids love them, no matter how they taste. How do they get those pictures inside? Couldn't you do something like this at home?
Yes, you can! Unless you've got a commercial-grade extruder with programmable patterns, they won't be exactly the same. They might be better!
The easiest pattern to make into sliced cookies is the pinwheel. These pinwheel cookies were made by Arundati at Escapades, where she posted the recipe. You make a layer of chocolate dough and a layer of vanilla dough, stack the two and roll them up together. When the roll is sliced, the cookies have a spiral pattern. It's the same concept as a jellyroll. But that's only the beginning of the patterns you can make.
Divide the dough into more pieces, and you can make more complicated patterns. Florence posted the recipe for her checkerboard cookies and the process for making them, with pictures. You cut the dough into blocks and stack them in a checkerboard pattern, then slice them as you would a roll of dough.
With more blocks and more colors, you can make even more complicated patterns. Eva Funderburgh makes pixelated cookies. With this method, patterns like these skulls and carrots are possible. The skull pattern is 9x9 pixels, or 81 colored rods of dough!
Funderburgh posted instructions for making your own pixel cookies at Instructables, and in this Flickr set, where you can see some more examples of the finished product. I love how the rods of dough are made using a Play-Doh extruder. Now you wish you hadn't thrown that out when your kids quit playing with it!
If you can make pixel cookies, the next step is to make fractal cookies. Windell at Evil Mad Scientist Laboratories took a process he used with clay and translated it into cookie dough. The result is these Sierpinski cookies (modeled on pattern of the the Sierpinski carpet). You start with somewhat the same process as the checkerboard cookies, but stretch out a portion of your finished block to a much smaller and longer size, then stack the smaller blocks together -and then do it again!
The limit to the "infinite fractal" comes at the point where you'd rather eat cookies than stretch cookie dough again!