Preheat the oven to 400°F. Have ready six ¼ pint (½ cup) mason jars on a baking sheet.
On a lightly floured surface, roll out the dough until it is flat and slightly thinner than it originally was. Cut the dough into six 3-inch circles and six 2-inch circles.
Press a 3-inch circle into a mason jar, pressing it firmly to the base and sides and taking care not to poke holes in the dough. Trim any excess from the top edge with a paring knife. Repeat with the remaining 3-inch circles and jars.
Scoop filling that has been cooked on woodstove ahead of time into the pastry-lined jars, mounding it about ½ inch over the top rim.
Place the 2-inch rounds over the filling and tuck the edges under so they meet the edge of the jar. Crimp the edges with your fingers or a fork. Chill the pies for 10 minutes.
While the pies chill, whisk the egg and water together to combine. Brush the egg wash over each pie top, and then sprinkle the top of each with ½ teaspoon berry sugar.
Cut small vents into the top of each pie with a paring knife. Bake until the pies are golden brown, 20 to 25 minutes. Cool for at least 10 minutes before serving.