In a medium bowl, combine softened butter, brown sugar, flour, cinnamon, and salt. Mix until slightly chunky and chill in the freezer for about 10 minutes.

In a large mixing bowl, cream together the unsalted butter and granulated sugar using a handheld mixer until light and fluffy, about 3-4 minutes. Add in the egg and egg yolk, mixing until smooth.

In a separate bowl, whisk together all-purpose flour, baking powder, cornstarch, and salt. Gradually blend this into the wet mixture until just combined.

Divide the dough into two parts. Spread one half in the bowl, layer half of the filling over it, and top with the second half of the dough and remaining filling. Fold gently to create swirls.

Using a large cookie scoop, portion about 2 tablespoons of dough for each cookie and place on a parchment-lined baking sheet. Freeze for 10 minutes.

Preheat oven to 350°F (175°C). Bake cookies for 10-12 minutes until edges are golden and centers look slightly soft. The aroma will fill the kitchen.

Allow cookies to cool on the parchment for about 5 minutes, then transfer to a wire rack to cool completely.