In the bowl of a stand mixer (or using a hand mixer with paddle attachment), combine the unsalted butter, granulated sugar, and light brown sugar. Beat on medium-high speed for 2 to 3 minutes until the mixture becomes light and fluffy. Add the vanilla extract and eggs, then beat for another 1 to 2 minutes until everything is well combined and the batter is creamy.

In a separate medium bowl, whisk together the cake flour, cornstarch, baking soda, baking powder, and kosher salt.

Gradually add the dry ingredients to the wet ingredients, mixing on medium speed for about 1 to 2 minutes. Be sure to stop a couple times to scrape down the sides and bottom of the bowl so all ingredients are evenly incorporated. Cover the dough and chill it in the refrigerator for one hour.

Meanwhile, preheat your oven to 350°F (175°C) and line two large baking sheets with parchment paper.

In another medium bowl, mix the softened butter, light brown sugar, cinnamon, and cake flour for the filling until smooth. Using a heaping teaspoon (about 2 teaspoons), scoop out portions of filling, roll them into balls, and place them on a separate lined baking sheet.

Once the dough has chilled, use a 1/4 cup measuring cup (or a very large cookie scoop) to portion out the dough. For each cookie: break the dough in half, create a small well in the center of one half, place one ball of filling into that well, then press the other half on top and pinch the seams tightly. Roll gently into a ball to ensure the filling is sealed inside.

Arrange the cookie dough balls on the prepared baking sheets about 2 inches apart. Bake for 11 to 13 minutes, until the tops are just set and the edges are lightly golden. Remove from oven and let them cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.

While cookies cool, prepare the glaze. Whisk together the powdered sugar, cinnamon, melted and cooled butter, and milk until the glaze is smooth and pourable. Place a piece of parchment paper under the cooling rack to catch drips, then spoon or drizzle the glaze over the top of each cookie. Let the glaze set for about 15 minutes. Then enjoy!