In a stand mixer with the paddle attachment (or using a hand mixer), beat the softened butter, granulated sugar, and brown sugar on medium-high speed for 2–3 minutes until light and fluffy. Add in the vanilla and eggs, one at a time, mixing for 1–2 minutes more until fully incorporated.

In a separate bowl, whisk together the cake flour, cornstarch, baking soda, baking powder, and kosher salt. Slowly add these dry ingredients to the wet mixture, mixing on low speed just until combined. Cover the dough and refrigerate for one hour — this helps the cookies hold their shape and prevents spreading.

In a medium bowl, stir together the softened butter, brown sugar, cinnamon, and cake flour until you have a smooth, thick filling. Roll this mixture into about 2-teaspoon-sized balls and place them on a parchment-lined baking sheet while you prep the cookie dough.

Using a ¼ cup measuring cup or a large cookie scoop, scoop out portions of the chilled dough. Break each dough ball in half and create a well in one half. Place one ball of the brown sugar filling inside, then press the other dough half over it and pinch the seams to seal. Gently roll it into a ball to fully encase the filling.

Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper. Place the cookie dough balls about 2 inches apart. Bake for 11–13 minutes, until the tops are set and the edges are lightly golden brown. Let the cookies cool on the sheet for 5 minutes, then transfer to a wire rack to cool completely.

While the cookies are cooling, whisk together the powdered sugar, cinnamon, melted butter, and milk until smooth. Place parchment under your cooling rack and spoon the glaze over each cookie, letting it drip down the sides for that classic Pop-Tart look. Let the glaze set for about 15 minutes before serving.