Step 1: Prepare the Dough

• In a large mixing bowl, combine the flour, sugar, and salt.
• Add the cold, cubed butter to the flour mixture. Use a pastry cutter or your fingers to work the butter into the flour until it resembles coarse crumbs.
• Add the egg and vanilla extract. Stir to combine.
• Slowly add ice water, one tablespoon at a time, and mix until the dough comes together into a ball. Avoid overworking the dough.
• Wrap the dough in plastic wrap and refrigerate for at least 30 minutes.

Step 2: Make the Brown Sugar Filling

• In a small bowl, mix the brown sugar, flour, cinnamon, and softened butter until smooth and combined. Set aside.

Step 3: Roll Out the Dough

• Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper.
• On a lightly floured surface, roll out the dough to about 1/8-inch thickness.
• Use a knife or a cookie cutter to cut the dough into rectangles (about 3×4 inches).

Step 4: Assemble the Cookies

• Spoon a small amount (about 1 teaspoon) of the brown sugar filling onto the center of half of the dough rectangles.
• Place the remaining dough rectangles on top of the filled ones, pressing the edges to seal. Use a fork to crimp the edges to ensure they stay sealed while baking.
• If desired, brush the tops of the cookies with a beaten egg for a golden, shiny finish.

Step 5: Bake

• Bake the cookies in the preheated oven for 12-15 minutes, or until the edges are golden brown.
• Let the cookies cool on a wire rack.

Step 6: Make the Glaze

• While the cookies cool, whisk together the powdered sugar, milk, vanilla extract, and a pinch of salt in a small bowl until smooth. Adjust the consistency by adding more milk if needed.
• Drizzle the glaze over the cooled cookies.

Step 7: Serve & Enjoy

• Allow the glaze to set for a few minutes before serving. Enjoy these Brown Sugar Pop Tart Cookies with a glass of milk or as a sweet treat any time of day!