01 - Whisk together flour, sugar, and salt in a large bowl until thoroughly combined.
02 - Add cold cubed butter to the flour mixture. Using a pastry blender or fork, cut the butter into the flour until the mixture resembles coarse crumbs with pea-sized butter pieces remaining.
03 - Gradually drizzle ice water into the mixture, stirring gently with a fork just until the dough begins to come together. Turn onto a lightly floured surface, knead gently 2-3 times, then form into a flat disk. Wrap tightly in plastic wrap and refrigerate for at least 30 minutes.
04 - Preheat oven to 400°F. Line a baking sheet with parchment paper and set aside.
05 - Combine strawberry jam with diced fresh strawberries in a small bowl. Stir until evenly distributed.
06 - On a lightly floured surface, roll out chilled dough to approximately 1/8-inch thickness. Using a 3 to 4-inch heart-shaped cookie cutter, cut out 16 heart shapes. Gather scraps and re-roll if necessary.
07 - Place 8 heart cutouts on the prepared baking sheet. Spoon approximately 1 tablespoon of strawberry filling into the center of each heart, leaving a 1/4-inch border around the edges.
08 - Whisk together the egg and 1 tablespoon water in a small bowl until smooth.
09 - Lightly brush the edges of the filled hearts with egg wash. Place remaining heart cutouts on top and press edges firmly to seal. Crimp edges with the tines of a fork to ensure a tight seal.
10 - Brush the tops of each hand pie with remaining egg wash using a pastry brush. Sprinkle coarse sugar evenly over the tops. Cut a small vent slit in the center of each pie to allow steam to escape during baking.
11 - Bake for 18 to 22 minutes or until the tops are golden brown and the filling is bubbly. Rotate the baking sheet halfway through for even browning.
12 - Let the hand pies cool on the baking sheet for 5 minutes before transferring to a wire rack. Serve warm or at room temperature.