Preheat the oven
Preheat your oven to 375°F and line a baking sheet with parchment paper.
Make the filling
In a small bowl, combine the brown sugar, cinnamon, flour, melted butter, and salt. Stir until smooth and crumbly—it should look like a thick brown sugar paste. Set aside.
Prepare the crusts
Roll out your two pie crusts into even sheets. Layer one on top of the other to ensure even sizing, then cut into 6 rectangles per crust (you’ll have 12 total).
Assemble the pop tarts
Spoon a small amount of the brown sugar filling onto six of the rectangles, leaving a small border around the edges.
Top each one with another rectangle of dough.
Use a fork to crimp the edges closed, then poke a few holes in the top with a fork so steam can escape.
Bake
Brush the tops lightly with melted butter and bake for 15–20 minutes, or until golden brown and crisp.
Make the glaze
While the pop tarts bake, whisk together powdered sugar, brown sugar, cinnamon, vanilla, and milk until smooth and creamy. Adjust consistency as needed—add a little more milk if too thick.
Finish and serve
Once the pop tarts are slightly cooled, drizzle or spread the glaze over the tops.
Sprinkle with flaky salt if you like that sweet-salty finish (highly recommend!).