Melt butter over medium to high heat in a medium skillet Add diced apples , brown sugar , cinnamon and salt .Cook for about 6-7 minutes , or until the apples are soft
Make a slurry with the corn starch and water , add it to the apples. cook the mixture until the liquid is thickened .Allow to cool before assembling the turnovers
Preheat oven to 400 degrees . Roll 1 sheet of the puff pastry out on a flour surface to a square about 12x12 . Cut into 4 equal portions
Place puff pastry squares on a parchment lined baking sheet . Brush the edges with egg wash
Place about 2 tablespoons of filling in the center of the square
Fold puff pastry into a triangle
Crimp edges with fork ,Cut a small vent hole on top
Brush with egg wash . If you like sprinkle with a cinnamon sugar mixture . Bake in preheated oven for 15 minutes
Once out of the oven carefully transfer to a cooling rack
Mix glaze adding a little milk at a time until it is to a consistency you like
Drizzle glaze over cooled turnovers