How to Make It
In a large bowl, whisk the flour with the confectioners’ sugar and salt. Cut in the butter using a pastry cutter or 2 knives until the mixture resembles coarse meal with some pea-size pieces of butter remaining. Using a wooden spoon, stir in the egg yolk and water until a shaggy dough forms. Turn the dough out onto a work surface and knead gently until smooth. Cut the dough in half and shape into 2 disks. Wrap the disks in plastic and refrigerate until chilled, about 1 hour.
In a medium bowl, toss the blueberries with the granulated sugar, flour, lemon juice, salt and cinnamon.
On a lightly floured work surface, roll out 1 disk of dough to a 16-by-9-inch rectangle, about 1/8 inch thick. Using a 4-inch plate as a guide, cut out 8 rounds from the dough. Spoon 2 tablespoons of the filling into the center of a dough round and fold the dough over to form a half-moon. Press the edge to seal, then crimp decoratively. Transfer the hand pie to a parchment paper–lined baking sheet. Repeat with all of the remaining dough and filling; space the pies 1 inch apart. Refrigerate the hand pies until well chilled, about 30 minutes.
Preheat the oven to 400°. Brush the hand pies with the beaten egg and sprinkle with turbinado sugar. Bake for 15 to 18 minutes, until golden; some of the juices will spill out. Let cool slightly. Serve warm or at room temperature.