Prepare Cinnamon Filling: In a medium bowl, combine softened butter, brown sugar, flour, cinnamon, and a pinch of salt. Mix until smooth and well-blended, then transfer to the freezer for about 10 minutes.

Mix Sugar Cookie Dough: In a large bowl, whisk together flour, baking powder, baking soda, and salt. In another bowl, beat softened butter and granulated sugar until light and fluffy. Add the egg and vanilla extract, mixing well before folding in dry ingredients.

Assemble Cookies: Divide dough in half, press one half into a greased dish, spread cinnamon filling, then cover with remaining dough. Swirl gently to create a marbled effect.

Chill Dough: Form dough into balls and chill on parchment-lined sheet for 10 minutes to maintain shape while baking.

Bake: Preheat oven to 350°F (175°C). Bake dough balls for 10-12 minutes or until edges are set and centers are slightly underbaked. Cool on wire rack.