Mix filling: In a medium bowl, stir together pumpkin purée, brown sugar, and pumpkin pie spice.
Prep: Preheat the oven to 350°F. Line a baking sheet with parchment paper. Set aside.
Roll out the dough: On a floured surface, roll out one disc of dough until about ⅛" thick, lifting and turning the dough occasionally to prevent it from sticking to the counter.
Cut shapes out: Use a knife or a pastry wheel to cut out rectangles that are roughly about 2.5"x3.5". For ghost shapes (or any other shapes), use a cookie cutter or trace a paper cutout with a knife. You'll need two matching pieces for every pop tart. Repeat with the other disc of dough. Press all the scraps together, re-roll, and repeat.
Transfer to baking sheet: Place one piece of dough cutout from each pair onto your lined baking sheet, leaving about 1-2" of space in between each one.
Add filling: Add about 2 tablespoonfuls of pumpkin filling to the middle of each piece of dough, leaving about ¾" of the edge empty.
Seal with top crust: Gently stretch the matching top piece of dough to make it slightly bigger and place it down on top of the filling. Use a floured fork to press down along the edges to seal.
Apply egg wash: Brush a layer of beaten egg on top of the dough.
Bake: Bake pop tarts for about 40 minutes or until they're golden brown. Let them cool while you prepare the icing.