In a small bowl, mix 4 tablespoons softened unsalted butter, ⅓ cup brown sugar, 1½ tablespoons flour, 2½ teaspoons cinnamon, and a pinch of salt until well blended.

In a larger bowl, cream together 1 cup softened but cool unsalted butter and 1⅓ cups granulated sugar until fluffy.

Stir in 1¾ teaspoons vanilla, the large egg, and large egg yolk until perfectly mixed.

In another bowl, combine 2¾ cups flour, ¾ teaspoon baking powder, 1 teaspoon cornstarch, and ¼ teaspoon salt.

Gradually add the dry ingredients to the wet ingredients, mixing until combined.

Form rounded teaspoons of dough and roll them in the cinnamon sugar mixture. Place them on a baking sheet.

Bake at 350°F (175°C) for about 10-12 minutes or until the edges are slightly golden.