Line a cookie sheet with parchment paper and set aside.
Combine the flour, baking powder, cinnamon, and salt in a small bowl and set aside.
Beat the butter, granulated sugar, and brown sugar with an electric mixer or stand mixer until light and creamy.
Add in the egg and vanilla extract and beat until combined.
Slowly add the flour mixture and beat until fully incorporated; don't overmix.
Use a large cookie scoop to scoop out the dough and roll it into balls evenly.
Then flatten each ball to about ¾ inch thickness.
Use the end of a butter knife to make a spiral shape on the top of each cookie.
Place on prepared cookie sheet about 2 inches apart to allow for spreading.
Preheat oven to 350ºF. While the oven is preheating, place the sheet of cookies into the freezer for 10 minutes to chill. (Chilling the dough helps to keep the cookies from spreading too much when baked.)
Once the oven is preheated, remove the cookie sheet from the freezer and bake in the oven for 12-14 minutes or until light golden brown.
Remove from oven and allow to cool.
While the cookies are cooling, combine the glaze ingredients in a bowl. Add 1 to 2 Tablespoons of milk for a glaze consistency that will easily brush onto the cookies.
Using a pastry brush, brush the cookies with the glaze. Allow the glaze to set for 5 minutes before serving.
Notes
Leftover cookies can be stored in an airtight container at room temperature for up to 3 days.