I always start by preheating my oven to 375°F and lining a baking sheet with parchment paper. Getting this step done early means I'm not scrambling once my pastry is filled and ready to bake. It also keeps the crust from sitting out too long and getting warm before it hits the oven.
In a small bowl, I stir together the pumpkin puree, brown sugar, pumpkin pie spice, and vanilla extract until smooth. I make sure there are no streaks of sugar left sitting at the bottom. This filling comes together in under two minutes and can sit on the counter while I prep the crust.
I roll each pie crust out slightly on a floured surface, then use a pizza cutter to cut four rectangles from each one, giving me eight total. I try to keep my cuts even so the tops and bottoms match up nicely later. Any dough scraps get set aside or rerolled if needed.
I spoon about two tablespoons of pumpkin filling onto four of the rectangles, leaving a half-inch border around the edges. Then I brush that border with egg wash before placing the remaining rectangles on top. I press the edges firmly with a fork to seal in the filling and prevent leaks.
Before baking, I brush the tops of each pop tart with the remaining egg wash for that golden, bakery-style shine. I poke a couple of small holes in the top of each one to let steam escape. Then they go into the oven for 20 to 22 minutes, until the crust is golden brown.
Once they're out of the oven, I move the pop tarts to a wire rack and let them cool all the way down. This step matters more than people think, because a warm pastry will melt the glaze right off. I usually give mine at least 20 to 30 minutes before touching the glaze.
While the pop tarts cool, I whisk powdered sugar, milk, and a pinch of pumpkin pie spice together until it's smooth and pourable. I spread a spoonful over each cooled pop tart and add a light dusting of cinnamon sugar on top. Letting the glaze set for a few minutes before serving keeps it from sliding off.