Make the crust: In a large bowl, whisk together the flour and salt. Cut in the cold butter and shortening using a pastry blender or your fingertips until the mixture resembles coarse crumbs. Gradually add the ice water, mixing until just combined. Do not overmix.
Chill the crust: Divide the dough in half, flatten each half into a disc, wrap in plastic wrap, and refrigerate for at least 1 hour, or preferably overnight.
Prepare the filling: In a medium saucepan, combine the chopped strawberries, granulated sugar, and lemon juice. Cook over medium heat, stirring occasionally, until the strawberries soften and release their juices, about 5-7 minutes. In a small bowl, whisk together the cornstarch and 2 tablespoons of cold water to make a slurry. Add the cornstarch slurry to the strawberry mixture and cook, stirring constantly, until the filling thickens, about 1-2 minutes. Remove from heat and let cool completely.
Assemble the pop tarts: On a lightly floured surface, roll out one disc of chilled dough to about ⅛ inch thickness. Use a heart-shaped cookie cutter (about 4 inches wide) to cut out shapes. Repeat with the second disc of dough.
Fill the pop tarts: Place half of the heart cutouts on a baking sheet lined with parchment paper. Spoon about 2 tablespoons of strawberry filling onto the center of each heart, leaving a small border around the edges.
Seal the pop tarts: Brush the edges of the filled hearts with water. Top with the remaining heart cutouts and press the edges firmly to seal. Crimp the edges with a fork. You can also use a smaller heart cutter to make vent holes in the top of each tart.
Bake: Bake the pop tarts in a preheated oven at 375°F (190°C) for 20-25 minutes, or until golden brown.
Make the glaze (optional): While the pop tarts are baking, prepare the glaze. Whisk together the powdered sugar, milk or cream, and vanilla extract until smooth and creamy. Add red food coloring, if desired.
Glaze and decorate (optional): Once the pop tarts have cooled slightly, drizzle them with the glaze and decorate with sprinkles, edible glitter, or other toppings.