Prepare the Cinnamon Filling by combining softened butter, brown sugar, a bit of flour, cinnamon, and a pinch of salt. Stir until smooth, cover, and freeze for 10 minutes.

Prepare the Sugar Cookie Dough by whisking together all-purpose flour, baking powder, baking soda, and salt. In another bowl, beat unsalted butter and granulated sugar until light and fluffy. Add in the egg and vanilla extract, mix until incorporated, then combine dry and wet ingredients.

Assemble the Cookies by splitting the dough in half. Flatten one half and spread dollops of cinnamon filling across the center. Cover with the second half, folding and twisting gently.

Chill the Dough by rolling into balls, approximately 2 tablespoons each, and freezing for another 10 minutes.

Bake the Cookies at 350°F (175°C) for 10-12 minutes until edges are golden and centers seem slightly undercooked. Cool on a wire rack.