In the bowl of a stand mixer fitted with the paddle attachment, beat together the light brown sugar, powdered sugar, and butter at medium speed until smooth and fluffy. Add the egg, milk, and vanilla and continue mixing until combined.

In a small bowl, whisk together the flour, salt, and baking soda to combine. Empty the flour mixture into the butter mixture and reduce the speed to low, mixing until they are *just* combined. Form the dough into a ball and then pat it out into a rough rectangle, cover it, and refrigerate it for 1 hour.

In food processor or blender, blend together all the ingredients except the flour until smooth. Transfer the mixture to a bowl or stand mixer and stir in flour by hand or at low speed until *just* combined. Set aside at room temperature.

Roll out the vanilla dough into a 12 x 9-inch rectangle on a lightly floured piece of parchment paper. Spread the surface with cinnamon filling, going all the way to the edges of the rectangle. Roll the dough up from the long edge into a log, using the paper to help you, and using a metal spatula if needed to keep the dough from sticking to paper.

Once rolled, discard the paper and roll the log a little more on clean work surface to make it 16 inches long and a uniform cylinder. Cover and refrigerate for 90 minutes.

Preheat the oven to 400 degrees and line 3 baking sheets with parchment paper. Slice the log into 1/4-inch thick slices and place each cookie slice on a baking sheet with about 2 inches of space between the cookies. Once all the sheets are filled with cookies, place the baking sheets in the oven and bake until the cookies *just* start to turn a very faint gold around the edges, about 10 minutes.

Remove the pan from the oven and allow the cookies to cool for 10 minutes before transferring them to a wire rack to cool completely.

Whisk together all ingredients until smooth. To drizzle the glaze with precision, empty into a sandwich-sized ziplock bag and seal it. Cut off a VERY small tip of the corner of the bag (it's better to be too small than too big, you can always cut a bigger hole if you need to). Squeeze the bag to get the icing to drizzle out in a consistent stream. You can also drizzle it by hand with a spoon for a less precise appearance.

Drizzle a zig-zag pattern over each cookie and allow the cookies to rest for 15 minutes to set and harden the icing before touching and serving. These will keep in an airtight container in the refrigerator for up to 1 week.