In a skillet, melt the 1 Tbsp butter.
Add the diced apples and cook about 5-10 minutes.
Turn the heat to low and add the brown sugar, cinnamon, and salt. Stir.
Add the lemon juice, vanilla, nutmeg, and apple pie spice. Cook until the mixture is soft and thick, then set aside to cool.
Preheat oven to 400°F.
Roll one pastry sheet to about an 11" square and cut into 4 equal squares. Repeat with the second sheet.
Spoon a little of the cooled apple mixture into the center of each square, leaving at least a 1/2" border.
Beat together the egg and water. Brush the edges lightly, fold the pastry over, and use a fork to press and seal the edges.
Transfer to a baking sheet, leaving about an inch or 2 between each pastry.
Using a knife, lightly cut 2-3 small slits in the tops of each pastry, then brush the tops with egg wash.
Place in the fridge for about 30 minutes (this helps the pastry not to leak).
Bake at 400°F for 20-23 minutes or until golden and puffed.
Prepare the glaze by whisking the powdered sugar, whipping cream, vanilla, and a dash of cinnamon.
Once the pastries come out and are still warm, drizzle the glaze all over. Cool and enjoy