Preheat your oven to 350°F (175°C).

In a small bowl, mix 4 tablespoons of softened unsalted butter, brown sugar, 1½ tablespoons of flour, 2½ teaspoons of cinnamon, and a pinch of salt until creamy. Set aside.

In a larger bowl, cream together 1 cup of unsalted butter, granulated sugar, pure vanilla extract, the large egg, and the egg yolk until light and fluffy.

Gradually add 2¾ cups of all-purpose flour, baking powder, cornstarch, and ¼ teaspoon salt. Mix until just combined.

Take a small amount of dough and form a ball. With your thumb, create a slight indentation in the center. Fill the indentation with the cinnamon mixture and cover it with more cookie dough, rolling it slightly to seal.

Place on a baking sheet lined with parchment paper, ensuring there’s space between each cookie.

Bake for about 12-15 minutes, or until the edges are just golden. Remove from the oven and let cool.