01 - Preheat your oven to 400°F. Line a standard baking sheet with parchment paper to prevent sticking and ensure easy cleanup.
02 - In a small mixing bowl, combine the raspberry jam, lemon juice, and cornstarch. Stir thoroughly until the cornstarch completely dissolves and the mixture is uniform.
03 - Lightly flour your work surface. Roll out the pie dough to approximately 1/8-inch thickness. Using a 3.5-inch heart-shaped cookie cutter, cut out 16 heart shapes. Gather and reroll scraps as necessary.
04 - Arrange 8 of the cut heart shapes on the prepared baking sheet, leaving space between each. Place approximately 1 tablespoon of the raspberry filling in the center of each heart, keeping it away from the edges.
05 - Lightly brush the edges of the filled hearts with water using your finger or a pastry brush. Top each with a remaining heart shape. Press the edges firmly together, then crimp with a fork to create a tight seal.
06 - Whisk together the egg and milk in a small bowl until blended. Brush the tops of each hand pie with the egg wash using a pastry brush. Sprinkle generously with granulated sugar.
07 - Using a sharp paring knife, cut a small slit or make a tiny X in the center of each pie. This allows steam to escape during baking and prevents the filling from bursting through.
08 - Bake for 16 to 18 minutes, rotating the baking sheet halfway through for even browning. The pies are done when they're golden brown and crisp. Transfer to a wire cooling rack and let cool for at least 10 minutes before serving.