In a mixing bowl, combine softened unsalted butter, brown sugar, flour, cinnamon, and a pinch of salt. Mix until smooth and chunky. Refrigerate for 10 minutes.

In a large bowl, cream together 1 cup of unsalted butter and 1 cup of granulated sugar until light and fluffy, about 3-4 minutes.

Add in 1 tablespoon of vanilla extract, 1 egg, and 1 egg yolk, mixing until well combined.

Whisk together 2 ¾ cups of all-purpose flour, 1 teaspoon of baking powder, 2 tablespoons of cornstarch, and ½ teaspoon of salt in a separate bowl.

Gradually add the dry mixture into the wet ingredients and stir gently until no flour streaks remain.

Divide the cookie dough in half and spread one half in a lined baking dish, then sprinkle half of the cinnamon sugar filling over it.

Spread the second half of the dough over the filling, then add the remaining cinnamon sugar mixture on top.

Using a cookie scoop, portion out 2 tablespoons of the dough on a parchment-lined baking tray and freeze for 10 minutes.

Preheat the oven to 350°F (175°C). Bake the dough balls for 10-12 minutes or until edges are golden brown.

Cool on baking sheets for 5 minutes, then transfer to a wire rack to cool completely.