01 - Whisk together flour, baking powder, and salt in a medium bowl until thoroughly combined.
02 - Beat softened butter and granulated sugar in a large bowl until light and fluffy, approximately 2-3 minutes.
03 - Add egg and vanilla extract to the butter mixture. Mix until fully incorporated and smooth.
04 - Gradually add dry ingredients to the wet mixture, mixing just until the flour disappears. Avoid overmixing.
05 - Divide dough in half. Roll each portion between parchment paper sheets into 1/4-inch thick rectangles.
06 - Brush each rectangle with melted butter. Sprinkle brown sugar and cinnamon evenly across the surface.
07 - Starting from the long edge, tightly roll each rectangle into a log. Wrap in plastic and refrigerate 1 hour.
08 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
09 - Cut chilled logs into 1/2-inch rounds. Place on baking sheets 2 inches apart.
10 - Bake 9-11 minutes until edges are lightly golden. Cool on sheets 5 minutes, then transfer to wire rack.
11 - Whisk powdered sugar, milk, and vanilla until smooth. Drizzle over cooled cookies and allow to set.