In a large bowl, whisk together the pumpkin purée and egg until smooth.
Add the brown sugar, pumpkin pie spice, and salt, and whisk again until everything is combined. Set aside.
CRUST
Preheat the oven to 400°F (204ºC). Line one large baking sheet with parchment paper or a silicone baking mat. Set aside.
On a lightly floured surface, roll out one pastry sheet. Using a pizza cutter or sharp knife, cut the sheet evenly into 6 large rectangles. These will be the bottoms of your pies.
Place the pie bottoms on the prepared baking sheet. If you feel they are crowded, use two large baking sheets (3 pies per sheet) instead.
ASSEMBLE HAND PIES
Spoon 6 Tablespoons of pumpkin pie mixture onto each of the 6 bottom rectangles, leaving about ¼" border around the edge for crimping. You may have a little bit of filling leftover, but can certainly use it all up by overfilling the crusts.
Roll out the second she of puff pastry. Cut into 6 rectangles. Place the top rectangles over the filled bottoms, slightly stretching the top layer if necessary (puff pastry is very sturdy and forgiving). Crimp the edges with a fork to seal. If some of the filling squishes out, that's ok.
Cut two small slits in the top of each hand pie, then brush with egg wash and sprinkle with the pumpkin pie spice/sugar mixture.
Bake the pies for 30 minutes, or until the tops are desired golden to dark brown color. Rotate the baking sheets once during bake time. Remove pies from the oven and allow to cool on the baking sheet until safe to handle and serve. Leftover hand pies can be stored in the refrigerator, wrapped tightly in plastic wrap, up to 5 days. Reheat in microwave or in a 300°F (149ºC) oven for 10-15 minutes.
Notes
Pumpkin: I always measure pumpkin purée with measuring cups as the moisture content can wildly change the weight measurements, depending on the brand.
All nutritional values are approximate and provided to the reader as a courtesy. Changing ingredients and/or quantities will alter the estimated nutritional calculations.