Preheat and Prepare:

1. Preheat your oven to 350°F (175°C).
2. Line a baking sheet with parchment paper.

Make the Dough:

1. In a mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.
2. Beat in the egg and vanilla extract until well combined.
3. Gradually stir in the all-purpose flour, baking powder, and salt until a soft dough forms.

Roll and Fill:

1. Turn the dough out onto a lightly floured surface. Using a rolling pin, roll it into a rectangle approximately 12 x 8 inches.
2. In a small bowl, mix together the brown sugar and ground cinnamon.
3. Spread the 2 tablespoons of softened butter evenly over the dough, then sprinkle the cinnamon sugar mixture on top.
4. Starting with the long edge, tightly roll up the dough into a log. Chill for 5 minutes if needed for easier slicing.

Slice, Bake, and Glaze:

1. Slice the log into 1/2-inch thick rounds and arrange them on the prepared baking sheet, spacing them slightly apart.
2. Bake for 10–12 minutes, or until the cookies are lightly golden around the edges.
3. Meanwhile, whisk together the powdered sugar and milk (or lemon juice) in a small bowl to form a smooth glaze.
4. Remove the cookies from the oven and let them cool for a few minutes on a cooling rack, then drizzle the glaze over each cookie.