Start by cutting your very cold unsalted butter into small, manageable pieces. In a large bowl, whisk together the flour and salt. Now, use a pastry blender or your fingertips to gently work the butter into the flour mixture until it resembles coarse crumbs with some pea-sized pieces. Slowly pour in about half of the cold water, mixing gently. Continue to add the remaining water, a tablespoon at a time, until the dough just comes together into a cohesive ball. Be careful not to overmix!
Form the dough into a ball, then divide it into four equal sections. Gently roll each section into a smaller ball and place them into separate resealable bags or cover with plastic wrap. Pop them into the fridge for about 10 minutes to chill, making them easier to handle.
On a lightly floured surface, roll out one of your chilled dough balls to about ⅛-inch thickness. Use a small heart-shaped cookie cutter (or a knife for freehand hearts!) to cut out little decorative hearts, roughly ½-inch in size. In a small bowl, whisk one egg white with 1 tablespoon of sugar and a few drops of red food coloring to create a vibrant glaze. In another bowl, whisk the remaining two egg whites with 3 tablespoons of sugar for a clear egg wash. Use a small pastry brush to delicately paint the red glaze over your tiny dough hearts. Set them aside to dry completely – this prevents the color from bleeding during baking.
Preheat your oven to 350°F (175°C). Roll out another dough ball to ⅛-inch thickness. Using a heart-shaped pie press (or a large heart cookie cutter if you're sealing by hand), cut out two large heart shapes. Place one large heart on each side of your pie press (or simply lay them flat if using a cutter). Lightly brush both heart pieces with the clear egg white mixture. Spoon about 1 tablespoon of the cherry pie filling onto the center of one heart, making sure to leave a clear border around the edges. Carefully close the pie press, pressing firmly to seal the edges of your hand pie. If using a cookie cutter, place the filling on one heart, top with the second, and crimp the edges with a fork to seal. Repeat this process until all your dough and filling are used, placing completed pies on a parchment-lined baking sheet.
Before baking, lightly brush each assembled cherry pie with the clear egg white wash. Gently place one of your dried red heart decorations on top of each pie. Sprinkle a generous amount of extra granulated sugar over the pies for a lovely sparkle and a touch of sweetness. Bake for 28-30 minutes, or until they turn beautifully golden brown. Once baked, let them cool completely on a wire rack. They're perfect for sharing as a thoughtful, homemade Valentine's treat!