01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
02 - In a small bowl, mix the raspberry jam, lemon juice, and cornstarch until well combined.
03 - On a lightly floured surface, roll out the pie dough to about 1/8-inch thick. Using a heart-shaped cookie cutter (about 3.5 inches wide), cut out 16 hearts.
04 - Place 8 hearts on the prepared baking sheet. Spoon about 1 tablespoon of the jam mixture onto the center of each.
05 - Brush the edges of the hearts with a little water. Place the remaining 8 hearts on top, gently pressing the edges to seal. Use a fork to crimp the edges securely.
06 - In a small bowl, whisk together the egg and milk. Brush the tops of the pies with the egg wash. Sprinkle with granulated sugar.
07 - Using a small knife, cut a tiny slit in the top of each pie for steam to escape.
08 - Bake for 16-18 minutes, or until golden brown and crisp. Cool on a wire rack before serving.