Prepare the Cinnamon Filling: In a small mixing bowl, combine softened butter, brown sugar, flour, cinnamon, and a pinch of salt. Mix until smooth. Transfer to plastic wrap and shape into a log. Freeze for 10 minutes.

Make Sugar Cookie Dough: In a large bowl, whisk together flour, baking powder, baking soda, and salt. In another bowl, beat softened butter with both sugars until light and fluffy. Add egg and vanilla extract, then gradually incorporate dry ingredients to form a soft dough.

Assemble Cookies: Divide dough in half, press one half into a disc. Slice the cinnamon filling into rounds and place on top of the dough. Layer the remaining dough over the filling and swirl together.

Chill the Dough: Scoop dough into balls about 2 tablespoons each on a parchment-lined baking sheet. Cover and freeze for 10 minutes.

Bake: Preheat oven to 350°F (175°C). Space chilled dough balls 2 inches apart on baking sheet. Bake for 10-12 minutes until edges set and centers are slightly undercooked. Cool on baking sheet for a few minutes before transferring to a wire rack.