01 - Whisk together flour, baking powder, and salt in a medium bowl. Set aside.
02 - Beat softened butter and granulated sugar in a large bowl until light and fluffy.
03 - Mix in egg and vanilla extract until fully incorporated.
04 - Gradually add dry ingredients to wet mixture, mixing just until dough forms.
05 - Divide dough in half. Roll each half between parchment sheets into 1/4-inch thick rectangles.
06 - Brush rectangles with melted butter, then sprinkle evenly with brown sugar and cinnamon.
07 - Tightly roll each rectangle from the long side into a log. Wrap in plastic and chill for 1 hour.
08 - Preheat oven to 350°F and line baking sheets with parchment paper.
09 - Cut chilled logs into 1/2-inch rounds and place 2 inches apart on prepared sheets.
10 - Bake for 9-11 minutes until edges are golden. Cool on sheets for 5 minutes, then transfer to wire rack.
11 - Whisk powdered sugar, milk, and vanilla until smooth. Drizzle over cooled cookies and let set.