Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.
Beat in the egg and vanilla extract until well combined.
In a separate bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon.
Gradually add the dry ingredients to the wet mixture, stirring until a dough forms.
Roll the dough into a log shape and refrigerate for about 30 minutes.
Once chilled, slice the dough into 1/2-inch thick rounds.
Place the slices on the prepared baking sheet, leaving space between each cookie.
Bake in the preheated oven for 10-12 minutes until the edges are lightly golden.
Remove from the oven and let cool on a wire rack. Drizzle with icing made from powdered sugar and a little milk.