Preheat your oven to 350°F (175°C). Line an 8x8 inch baking pan with parchment paper, allowing some excess paper to hang over the edges for easy removal after baking.
In a large mixing bowl, whisk together the flour, salt, and baking powder until well combined. Add the cold, cubed butter, and use a pastry cutter or your fingers to mix until the mixture resembles coarse crumbs. Stir in the granulated sugar, packed brown sugar, beaten egg, vanilla extract, and milk, mixing until a smooth dough begins to form.
Set aside one-third of the dough for later use as the top crust. Use the remaining dough to evenly press into the bottom of the prepared baking pan, forming a solid base.
In a small bowl, combine the packed brown sugar, ground cinnamon, and flour for the filling. Mix well, then evenly sprinkle this sweet mixture over the dough base in the pan.
On a lightly floured surface, roll out the reserved one-third of the dough to match the size of the baking pan. Gently place this rolled-out dough over the cinnamon filling. Cut slits in the top dough to allow steam to escape, or poke it with a fork for a rustic texture.
Transfer the pan to the preheated oven and bake for 25-30 minutes, or until the top is a beautiful golden brown.
Once baked, remove the pan from the oven and let it cool in the pan for about 10 minutes. Use the overhanging parchment paper to lift the bars out of the pan and allow them to cool completely on a wire rack.
In a medium-sized bowl, whisk together the powdered sugar and milk until the mixture is smooth and glossy. If necessary, add more milk to achieve your desired glaze consistency.
Once the bars have cooled down, drizzle the prepared glaze over the top. For an extra touch, dust with additional cinnamon if desired.
Cut into squares or rectangles for serving. Enjoy these delightful and sweet homemade pop tart bars with friends and family!
Notes
For a rustic texture, poke the top dough with a fork.