Step 1: Prepare the Dough

1. In a medium bowl, whisk together flour, baking powder, and salt.
2. In a large bowl, beat softened butter and sugar until light and fluffy.
3. Add the egg and vanilla extract, mixing until combined.
4. Gradually add the dry ingredients and mix until a soft dough forms.
5. Wrap the dough in plastic wrap and refrigerate for at least 30 minutes to firm up.

Step 2: Make the Cinnamon Filling

1. In a small bowl, mix melted butter, brown sugar, and cinnamon until combined.

Step 3: Roll & Fill the Dough

1. Roll out the chilled dough on a lightly floured surface into a rectangle (about ¼-inch thick).
2. Spread the cinnamon filling evenly over the dough.
3. Carefully roll the dough into a tight log, starting from the long side.
4. Wrap the log in plastic wrap and refrigerate for another 30 minutes.

Step 4: Slice & Bake

1. Preheat oven to 350°F (175°C).
2. Unwrap the dough and cut it into ¼-inch slices.
3. Place slices on a parchment-lined baking sheet, spacing them slightly apart.
4. Bake for 10–12 minutes, or until the edges are lightly golden.
5. Let cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack.

Step 5: Drizzle with Glaze

1. In a small bowl, whisk together powdered sugar, milk, and vanilla until smooth.
2. Drizzle the glaze over cooled cookies using a spoon or piping bag.