For the Cookie Dough:

1 cup (227g) unsalted butter, softened

1 cup (200g) granulated sugar

1/2 cup (100g) brown sugar

2 large eggs

2 teaspoons vanilla extract

3 cups (375g) cake flour

2 teaspoons cornstarch

1 teaspoon baking soda

1/2 teaspoon baking powder

1/2 teaspoon salt

For the Brown Sugar Filling:

1/4 cup (57g) unsalted butter, softened

1/2 cup (100g) brown sugar

1 teaspoon ground cinnamon

2 tablespoons cake flour

For the Cinnamon Glaze:

1 cup (120g) powdered sugar
1/2 teaspoon ground cinnamon

2 tablespoons unsalted butter, melted

2–3 tablespoons milk

Prepare the Dough:
- Cream together the softened butter, granulated sugar, and brown sugar until light and fluffy (2-3 minutes).
- Add eggs one at a time, mixing well after each addition. Stir in vanilla extract.
- In a separate bowl, whisk together cake flour, cornstarch, baking soda, baking powder, and salt.
- Gradually mix dry ingredients into the wet mixture until just combined.
- Cover and refrigerate dough for at least 1 hour.
Make the Filling:
- Mix butter, brown sugar, cinnamon, and cake flour until a soft paste forms.
Assemble & Bake:
- Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
- Scoop 2 tbsp of cookie dough, flatten slightly, and add a small amount of filling in the center. Cover with another flattened piece of dough and seal the edges.
- Place cookies on the baking sheet with space between them.
- Bake for 10-12 minutes until edges are set and lightly golden.
- Cool on the baking sheet for 5 minutes before transferring to a wire rack.
Prepare the Glaze & Finish:
- Whisk together powdered sugar, cinnamon, melted butter, and milk until smooth.
- Drizzle over cooled cookies and allow to set before serving.

Storage: Keep in an airtight container at room temperature for 4 days or refrigerate for up to a week.

Freezing: Freeze unglazed cookies for up to 2 months; thaw before glazing.

Make-Ahead: Dough can be chilled for up to 48 hours before baking.