01 - In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, and salt. Cut in the cold cubed butter using a pastry cutter or two knives until the mixture resembles coarse crumbs with pea-sized pieces of butter remaining.
02 - Gradually drizzle in the ice water, stirring gently until the dough just comes together. Divide the dough into two equal disks, wrap each tightly in plastic wrap, and refrigerate for at least 30 minutes to firm up.
03 - In a medium saucepan, combine the diced peaches, granulated sugar, lemon juice, and cornstarch. Cook over medium heat, stirring frequently, for 5 to 7 minutes until the mixture thickens and becomes glossy. Remove from heat and let cool completely.
04 - Preheat the oven to 400°F (200°C). Line a large baking sheet with parchment paper and set aside.
05 - On a lightly floured surface, roll each chilled dough disk to approximately ⅛-inch (3 mm) thickness. Cut into 3×4 inch (8×10 cm) rectangles, yielding 16 total rectangles.
06 - Place 8 dough rectangles on the prepared baking sheet. Spoon about 1 rounded tablespoon of the cooled peach filling into the center of each rectangle, leaving a ½-inch border around the edges.
07 - Lightly brush the exposed borders with beaten egg wash. Place a second dough rectangle over each filled one and press the edges firmly with a fork to crimp and seal.
08 - Brush the tops of each assembled pop tart with the remaining egg wash. Prick the tops 3 to 4 times with a fork to create steam vents during baking.
09 - Bake in the preheated oven for 20 to 25 minutes, or until the pastry is golden brown and flaky. Transfer to a wire rack and allow to cool completely.
10 - In a small bowl, whisk together the powdered sugar, milk, and vanilla extract until smooth and pourable. Drizzle or spread the glaze over the cooled pop tarts. Top with colored sprinkles if desired. Allow the glaze to set before serving.