Preheat your oven to 350°F (175°C) and prepare two baking sheets lined with parchment paper.

Whisk together the flour, baking powder, and salt in a medium bowl until well combined.

In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.

Add in the egg and vanilla extract, beating until fully combined.

Gradually mix the whisked dry ingredients into the wet mixture until no visible flour streaks remain.

In a small bowl, combine brown sugar with ground cinnamon.

Roll out the dough into a rectangle about 1/4-inch thick.

Sprinkle the cinnamon-sugar filling over the rolled-out dough, leaving a small border.

Roll the dough tightly into a log shape, wrap in plastic wrap, and chill for about 30 minutes.

Slice the log into 1/4-inch thick rounds and place them on prepared baking sheets.

Bake for 10-12 minutes or until edges are lightly golden.

Cool on sheets for a few minutes before transferring to wire racks.

Whisk together confectioners' sugar, milk, and vanilla extract until smooth for the icing.

Drizzle the icing over the cooled cookies and let it set before serving.