01 -
Beat the softened butter and granulated sugar until creamy, about 2 minutes. Mix in the egg and vanilla. Add the flour, baking powder, and salt, then mix on low just until a soft dough forms.
02 -
Place the dough between two sheets of parchment and roll it into a rectangle about 10 by 13 inches and 1/4 inch thick. Trim rough edges if needed.
03 -
Spread the very soft butter over the dough, leaving a 1/2-inch bare strip along one long edge. Stir the brown sugar, cinnamon, and flour together, then sprinkle evenly over the butter.
04 -
Starting on the long side opposite the bare strip, roll the dough into a snug log. Wrap tightly in parchment or plastic wrap and chill for at least 1 hour, until firm.
05 -
Heat the oven to 350°F (175°C) and line two baking sheets with parchment. Slice the chilled log into 1/2-inch rounds and place them 2 inches apart.
06 -
Bake for 10-12 minutes, until the edges are set and just starting to turn golden. Cool on the baking sheet for 5 minutes, then move to a wire rack to cool completely.
07 -
Whisk the powdered sugar, milk, vanilla, and salt until smooth. Drizzle over the cooled cookies and let the glaze set for about 20 minutes before serving.