Preheat the oven to 400 degrees F.
On a parchment paper-lined cookie sheet with sides, lay out the round of pie dough. With a small sharp knife, cut the round into the shape of a heart. Reserve the scraps of dough that are left over from making the cuts (to use for a "patch" or "dough extension" when folding the crust over the filling in the top middle section of the heart).
Spoon the apple pie filling on to the middle of the pie dough leaving about 3 inches of empty space from the edges of the dough. Top the pie filling with small cubes of butter.
Fold the edges of the dough (the part without any filling on it) inwards to form a “heart” around the filling.
At the top of the heart, in the middle, use the scraps of dough to make an extension wide enough to fold dough inwards over the filling. Pinch a few of the scraps into the existing dough (in the top/middle part of the heart). Then mold it into an edge that can be folded evenly with the existing edges of each top side of the heart.
Adjust the dough around the perimeter of the heart if needed so that the amount of dough folded over the filling is about the same width.
For the Egg Wash - in a small bowl, whisk together egg and cold water. Brush the egg wash on the dough. Right after brushing the egg wash on the dough, sprinkle sanding sugar (or other type sugar with large crystals) on top of the dough (so that it will stick).
Top the apple pie filling with streusel.
Bake in a preheated oven until the pastry turns a light golden brown (about 33 minutes). It’s okay if the juice from the apples seeps out of the crust on to the parchment paper while baking.
Remove from the oven and let cool a bit before serving. Serve warm, topped with vanilla ice cream and candy sprinkles (optional).