In a large bowl, whisk together flour and salt. Cut in cold butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs with some pea-sized pieces of butter remaining.
Gradually add ice water, 1 tablespoon at a time, mixing until the dough just comes together. Do not overmix.
Divide the dough in half, flatten each half into a disc, wrap in plastic wrap, and refrigerate for at least 30 minutes.
While the dough is chilling, prepare the filling. In a small bowl, mix together brown sugar, cornstarch, and cinnamon. Stir in melted butter until well combined.
Preheat oven to 400°F (200°C). Line baking sheets with parchment paper.
On a lightly floured surface, roll out one disc of dough into a 10x12 inch rectangle. Cut into 6 equal rectangles.
Spread the brown sugar filling evenly over 3 of the dough rectangles, leaving a small border.
Top with the remaining 3 dough rectangles. Crimp the edges with a fork to seal.
Transfer the pop-tarts to the prepared baking sheets. Cut small slits in the top of each pop-tart to allow steam to escape.
Bake for 18-20 minutes, or until golden brown.
While the pop-tarts are baking, whisk together powdered sugar, milk, and vanilla extract for the glaze until smooth.
Let the pop-tarts cool on the baking sheets for a few minutes, then transfer them to a wire rack. Drizzle with glaze while still warm.
Notes
Store cooled pop-tarts in an airtight container at room temperature for up to 3 days.