For the Filling:

1. In a small bowl, whisk together the sugar and cornstarch. Combine the fruit and sugar/cornstarch mixture in a medium saucepan. 
2. Cook the fruit over medium heat, stirring constantly with a sturdy spoon or spatula, until the fruit softens and the liquid is thick and shiny, about 10 to 12 minutes. The liquid in the mixture should not be runny, and it should thickly coat the back of the spoon.
3. Stir in the lemon juice, and set the filling aside to cool completely. The filling can also be prepared a day ahead and stored in the refrigerator in an airtight container until you are ready to assemble the pies.

For the Pastry:

1. Whisk the flour and salt together in a large bowl. 
2. Use a pastry cutter to cut and mix the cubed butter into the flour and salt mixture, until it resembles cornmeal with some larger crumbles that are about the size of peas, and until each piece of butter is entirely coated in flour.
3. With your hands, knead in 1/8 cup cold water. Mix just until a dough starts to form. If the dough feels too dry and crumbly, add the additional 1/8 cup of water.
4. Form into a flat disc, cover completely in plastic wrap, and chill for 1 hour in the refrigerator. 

To Assemble and Bake:

1. Line a baking sheet with parchment paper or a silicone mat. Set aside.
2. Once the dough is chilled, lightly flour a clean countertop with more einkorn flour and place the unwrapped chilled disc on top. Let the disc sit at room temperature for 10 minutes. Lightly dust the top of the disc with more flour. With a rolling pin, roll out and flatten the dough into a large circle until it is about 1/8 inch thick.
3. Using a floured 6-inch round cookie cutter, cut out circles. Re-roll the dough only once and cut out a few more circles. You should have a total of 8 circles. 
4. Spoon 1 tablespoon of the chilled fruit filling in the center of each circle, leaving a clean border around the edge about 1/2 inch wide. 
5. Set a small bowl filled with 1 tablespoon of water next to you. With your finger or a small brush, lightly coat the border with a very thin film of water. Seal the edges with the tines of a floured fork. Carefully transfer to the prepared baking sheet, and repeat with the remaining circles, leaving about an inch between each pie on the baking sheet.
6. Transfer the baking sheet uncovered to the refrigerator. Refrigerate the hand pies until fully chilled and hardened, about 1 hour. 
7. While the dough is chilling, preheat the oven to 375°F. Whisk together the egg with the remaining 1 tablespoon water in a small bowl to make an egg wash.
8. When fully chilled, remove the baking sheet from the refrigerator. Lightly brush the egg wash on top, and generously sprinkle with turbinado sugar. Use a sharp knife to cut one or two narrow slits in the top of each pie.
9. Bake for 25 to 30 minutes, until lightly browned on the outside. Remove from the oven and let cool for 10 minutes on the pan before transferring to a cooling rack. Serve while still warm, or at room temperature.