¾cup(170g) unsalted buttersoftened to room temperature
¾cup(90g) powdered sugar
1large egg yolkreserve the egg white for the filling
reserved egg white
¼cup(50g) granulated sugar
½cup(60g) powdered sugar
2Tablespoons(30mL) milk or cream
In a medium size bowl, whisk together the flour, salt, and baking powder. Set aside.
In a large bowl with a handheld mixer or the bowl of a stand mixer fitted with the paddle attachment, cream the butter and powdered sugar until light and fluffy, about 2-3 minutes. Add the egg yolk (reserving the egg white) and the vanilla and beat until everything is incorporated, scraping down the sides as necessary.
With the mixer on low, slowly add the dry ingredients to the wet ingredients until it just comes together.
Liberally dust a portable flat surface, like a baking sheet or large cutting board, with powdered sugar, then flatten the dough into a 9" x 12" rectangle, about ¼" in thickness.
Whisk together the reserved egg white and the water, then brush over the flattened cookie dough.
Toss together the granulated sugar and the cinnamon until evenly combined, then sprinkle evenly over the brushed cookie dough.
Working with the 12" side, slowly and gently roll the dough into a tight 9" long log. I like to use a large bench scraper or large cake lifter to help me do this. If your dough is too soft to roll, stick it in the refrigerator for about 5-10 minutes to stiffen the butter (this is why it is on a portable flat surface).
When you have formed the log, cover the log with plastic wrap or a clean kitchen towel, then chill in the refrigerator at least 2 hours and up to 2 days. This is easiest if you place it on something flat that fits in the fridge.
When you are ready to bake the cookies, preheat the oven to 350ºF (177ºC). Line a large baking sheet with parchment paper or a silicone baking mat. Set aside.
Remove the dough from the refrigerator and, using a sharp knife, cut into ½" slices and place on prepared baking sheet.
Bake the cookies for 12-14 minutes, until edges just start to brown. Remove from the oven and allow to rest on the baking sheet at least 5 minutes before transferring to a wire cooling rack to cool completely before icing.
In a small bowl, whisk together the powdered sugar, milk, vanilla, and cinnamon until smooth.
Drizzle the icing over cooled cookies, then allow to icing to set (about 1 hour). Cookies stay fresh covered tightly at room temperature up to 5 days. Baked cookies (iced or not iced) freeze well, up to 3 months.
Make ahead: rolled dough log can be wrapped tightly and frozen up to 3 months. Thaw in the refrigerator overnight, then proceed with recipe.