In a large bowl, combine the flour, sugar, and salt. Stir until evenly mixed.
Add the grated frozen butter. Using your fingertips, gently rub the butter into the flour mixture, leaving some small pieces of butter throughout. Be careful not to overwork the dough or let the butter melt.
Add the cold cream and water. Use a knife to cut the liquid into the flour mixture until a shaggy dough forms. If the dough seems too dry, add cold water 1 teaspoon at a time. The dough should mostly hold together while still having a few dry spots.
Bring the dough together and divide it into two rounds. Wrap each one in plastic wrap and chill in the refrigerator for at least 30 minutes.
In a bowl, whisk together the pumpkin puree, brown sugar, heavy cream, egg, pumpkin pie spice, vanilla, and salt until smooth.
Transfer the mixture to a small pot and cook over medium-low heat, stirring constantly, for about 5–7 minutes. The filling should become darker and thick enough to mostly hold its shape on a spoon.
Remove from the heat and let the filling cool completely before assembling the pies.
Line baking sheets with parchment paper. Whisk the remaining egg with 2 teaspoons of water to make the egg wash.
Work with one portion of dough at a time. Roll the dough between two pieces of lightly floured parchment until it is about ¼-inch (6mm) thick.
Cut the dough into 2 ½- to 3-inch (8–9cm) rounds. You can use a fluted cutter if you want decorative edges. Try to get as many rounds as possible from the first roll. You can reroll the scraps, but keep in mind that the dough can become tough and lose some of its flakiness if it is worked too many times.
Place half of the dough rounds on the prepared baking sheets. Spoon about 2 tablespoons (30g) of pumpkin filling into the center of each round.
Brush the edges around the filling with a little egg wash. Place another dough round over the top and gently press around the edges to seal. Press out any trapped air and make sure there are no gaps where the filling can leak.
For an extra seal, press around the edges with the tines of a fork.
Brush the tops with egg wash and sprinkle with raw cane sugar. Use a sharp knife to cut 2–3 small vents in the top of each pie.
Chill the assembled pies in the refrigerator for 15 minutes.
About 10 minutes before baking, preheat the oven to 375°F (190°C).
Bake the hand pies for 25–30 minutes, or until the edges are golden brown.
Remove from the oven and let them cool completely before serving.