Sift together the flour and cinnamon (if using) in a mixing bowl, and set aside.

Using a stand mixer fitted with a paddle attachment, cream together the butter and sugar. Mix for about 3 minutes on medium speed until the mixture is light and fluffy.

Turn the mixer speed to low and add in the cold egg. Mix until completely incorporated, around 30 seconds.

Then add in your flavoring extracts, and mix for about 20 more seconds. It is important to use clear flavoring extracts, as to not alter the color of the dough.

Next, gradually add in the flour mixture until completely combined.

Shape the dough into a ball and divide it in half. I used a kitchen scale to be extra-precise and evenly divide it.

Add a very, very small amount of black food coloring to one half of the dough to get a light-grey color. If you don’t color it, the dough will bake as an off-white color – if you don’t mind this, then omit the coloring on this step. Knead the color into the dough using gloved hands, or return it to the mixing bowl until combined.

For the second half of the dough, do the same, adding more food coloring to get a deep black color. It doesn’t take much – remember that the dough will get much darker as it chills in the refrigerator.

Pat each section of dough into a disc-shape, wrap with plastic wrap, and allow to chill in the refrigerator for 30-45 minutes.

Once the dough has chilled, place the black cookie dough on a piece of parchment paper. Using your hands, shape the dough into a rectangle shape.

Using a rolling pin, roll the dough out to 1/4″-thick, into an approximately 8″x9″ rectangle. I used rolling pin guide rings, but using 1/4″ wooden dowels on each side works great, too.

Repeat the same steps with the light grey cookie dough.

Once both pieces of dough are rolled out, place the light grey dough right on top of your black dough. Lightly use your rolling pin to ensure that they are firmly stuck together.

From the short end of the dough, very carefully start rolling it up, like a jellyroll. It’s important to try to get the dough as tight as possible. Use your parchment paper to guide the dough and prevent it from sticking to your hands.

After the dough is rolled up, wrap the cookie dough log in parchment paper, and twist the ends (like a candy wrapper). You can use twist-ties or rubber bands to hold it in place. Place the cookie dough log upright in a tall drinking glass – this will help the dough to retain it’s roundness. Chill in the freezer for at least 60 minutes, or in the refrigerator for 2-3 hours.

When ready to bake, preheat your oven to 325° (F). Unwrap the dough and slice into 1/4″ slices using a sharp knife.

Pour your nonpareils into a bowl (or, use coarse sugar). Roll the edges of the cookie slices to coat, and place the slices onto a parchment-lined baking sheet.

Bake for 12-15 minutes. Allow to cool for 5 minutes on the cookie sheet before transferring to a cooling rack.