Sierpinski Triangle Fractal Cookies

Sweet, buttery, dark and minty, these cookies are more than just fabulously nerdy.

A few years ago, I was inspired by some fractal cookies on Evil Mad Scientist.  I decided to make a triangular version.  I wasn't an instructables member back then, so I didn't think of taking pictures of the step by step process.  I did upload pictures of my cookies to our flickr stream, though.

Now that it's holiday cookie season, I figured it was time to make another batch.

I'm particular about cookie recipes.  I won't use shortening or artificial flavoring.  This recipe is adapted from Alton Brown's sugar cookie recipe.

You will need:

1 C plus 2 T butter
1 C granulated sugar
1 egg
3 C flour
3/4 t baking powder
1/4 t salt
1 T milk
1-3 t vanilla extract
1-2 t peppermint mint extract
1/2 C powdered sugar
1/2 C cocoa powder (I used the extra dark)
a few drops green food coloring

Soften the butter if you haven't already.  Melting the butter would change the texture of the cookies.  Don't do that here.

Beat 1 C of the butter until it becomes fluffy and lighter colored.  Add the granulated sugar and keep beating.  The sugar granules cut air pockets into the butter, which helps make a nice structure for the cookie and helps incorporate the other ingredients evenly.

Add the egg and beat more.  The dough usually gets gooey and then fluffy again when you add the egg.

Mix the flour with the salt and baking powder in a bowl, then add that mixture to the butter mixture, along with the milk and vanilla.

Mix very thoroughly.  The dough will be crumbly looking at first, but should come together.  You should be able to squish it together, but it shouldn't be so soft that it can't hold its shape.

Divide the dough roughly in half.

Add a few drops of green food coloring, the peppermint extract, and the powdered sugar to one portion and mix well.  I messed this up and added the powdered sugar to the whole batch.  Don't do this.  You want to add extra sugar to the non cocoa part because the two doughs need to be about the same texture when raw.  Cocoa powder stiffens the cocoa dough, so adding powdered sugar to the green dough helps a bit.

Soften (or, heck, melt) the reserved 2 T butter and mix into the other portion of dough, along with the 1/2 C cocoa powder.  The butter helps soften this half of the dough to match the softness of the green dough.

This is where these cookies become a bit of a pain.

A long, straight knife and parchment paper help some.

Pull off a good bit of the cocoa dough.  I used half the cocoa dough here.  Roll it into a log on parchment paper.  Fold the parchment paper around the log, then gently press a long knife against one side, pressing the other side of the dough with your hand.  Carefully shape the dough into a triangular log this way.

You might decide to unwrap the parchment to check on the angles of the triangle.

Once it looks the way you want, slice the log into three sections.  Now pull off a piece of green dough, using about 1/3 as much as the cocoa dough you rolled.  Roll this into a triangular log, making sure it's the same size as the cocoa logs.

This is probably a good time to preheat your oven to 350 degrees F.

Lay two cocoa triangular logs side by side with edges touching.  Gently lay the green triangular log, point side down, between the two.  Set the third cocoa log on top of the green log, flat side down.

Make sure the green dough isn't poking out of the sides of the log, or the triangles will get distorted.  This is when it becomes important for the two doughs to have the same consistency.  Press the sides of the log, keeping them straight, but lengthening it.  It helps to wrap the log in parchment and use a flat knife or dough scraper.

Cut the log into three roughly equal segments.  Repeat as you did for the first part of this step; lay two of the segments next to each other with edges touching.  Make a green triangle log the same size as each of these, placing it between the two logs, point down.  Lay the third log on top.

Don't go too far with the fractal iterations, or you'll lose the detail of the triangles.  When you have enough triangles in your cookies, lengthen the triangular log until it seems like the right size.

Your oven should be preheated now.  Using a sharp knife, slice the cookies from the triangular log.  Be careful not to warp the pattern inside.  Carefully place them on a sheet of parchment and bake for about 8 or so minutes (depending on your oven and the thickness of the cookies) until they're no longer squishy, but not quite ready to brown at the edges.

They'll probably be slightly golden brown on the underside; that's okay.


The ends of your logs probably have some really distorted dough.  Slice this and bake it, too; the cookies will still taste good.  You can always roll up any remaining scraps of dough and make swirly cookies.

I recommend serving these with mint hot chocolate.  Thanks for reading!