Make the dough: Whisk together flour, baking powder, and salt. In a large bowl, cream butter and sugar until fluffy. Mix in egg and vanilla, then gradually add dry ingredients until a soft dough forms.

Chill: Divide dough in half, shape into rectangles, and wrap in plastic wrap. Chill for at least 1 hour.

Prepare filling: Mix brown sugar and cinnamon in a small bowl. Melt butter separately.

Roll and fill: Roll out one dough portion into a rectangle. Brush with butter, sprinkle with cinnamon-sugar, and roll tightly into a log. Wrap and chill for 30 minutes. Repeat with second portion.

Slice and bake: Preheat oven to 350°F (175°C). Slice logs into ½-inch rounds and place on lined baking sheets. Bake 10–12 minutes, until edges are lightly golden.

Cool and glaze: Cool cookies on a wire rack. Whisk glaze ingredients and drizzle over cooled cookies if desired.