Add in your apples, lemon juice, water, brown sugar, and cinnamon.
For the cornstarch, make it into a slurry before adding it to the sauce pan - mix it with some water until it fully dissolves and then add it in. (This will prevent clumps).
Let the mixture simmer for about 7-10 minutes on low medium heat until the apples soften and the mixture thickens.
Frosting
Mix together your powdered sugar, vanilla extract, soy milk, and butter (melted) until its a smooth consistency.
Assembly
Cut up your pastry dough into 6 pieces. This will make 3 pastries.
Place your filling into the center of 3 of the pieces, making sure to stay an inch away from the edges. We don't want the filling to spill out!
Wet the edges of the pastry sheet with some water using your finger to trace the edges. Put the other sheets without the filling on top and press the edges firmly to close off the pastry.
Using a fork, poke three sets of holes in the center of the pastry about an inch apart for some ventilation. You can also use the fork to gently press the edges down further.
Put your pastries in the oven at 375 degrees for 20-22 minutes.
Wait until the pastries cool down, add your glaze on top, and serve!