In a mixing bowl, whisk together 2 cups of all-purpose flour, 1 teaspoon of baking powder, ½ teaspoon of baking soda, and ¼ teaspoon of salt until well combined.

In a separate bowl, cream ½ cup of unsweetened butter with ¾ cup of brown sugar and ¼ cup of granulated sugar until fluffy.

Add 1 large egg and 1 teaspoon of vanilla extract, mixing until smooth.

Gradually add the dry mixture to form a soft dough.

Divide the prepared dough into two equal disks and wrap each in plastic wrap.

Refrigerate for at least 1 hour, allowing the dough to stiffen and making it easier to roll out later.

In a medium bowl, combine ½ cup of brown sugar, 1 tablespoon of cornstarch, and 1 teaspoon of cinnamon.

Mix well until the ingredients are evenly distributed.

Preheat your oven to 350°F (175°C).

Once chilled, take one disk of dough and place it on a floured surface.

Roll it out to about ¼ inch thick.

Cut the dough into rectangles, roughly 3x4 inches.

Repeat with the second disk of dough.

Place approximately 1 tablespoon of the filling in the center of half of the rectangles.

Carefully cover each filled rectangle with another dough piece, pressing the edges to seal.

Use a fork to crimp the edges securely.

Transfer the assembled cookies onto a lined baking sheet.

Brush the tops lightly with milk.

Bake in the preheated oven for 12-15 minutes, or until the edges are light golden brown.

While the cookies cool, mix together 1 cup of powdered sugar with 1-2 tablespoons of milk until smooth.

Drizzle the icing over each cookie for a sweet finishing touch.