Using a food processor, pulse together the flours, salt and cinnamon until combined. Add butter and pulse until mixture becomes coarse meal, about 15 pulses.
Mix together the water and vodka. Add to the food processor and pulse until it starts to clump together. DO NOT pulse until ball is formed. It should be crumbly with large clumps of dough.
Turn dough only a lightly floured surface and form into a ball. Cut in half and then press each into a flat disk. Cover with plastic wrap and refrigerate for an hour.
While dough is resting, make the apple filling. Heat butter in medium skillet over medium heat. Add apples, sugar, lemon juice, cinnamon and salt. Cook for about 10 minutes or until apples are soft. Add cornstarch to thicken. Remove from heat and let cool. Add to food processor and puree until smooth.
Once ready, lightly flour a clean surface. Take out ½ the dough and roll the crust down to ⅛" thick and 9x12" in size. Cut into 3x4" pieces so you'll end up with 9 rectangles. Using a spatula, transfer the rectangles to a parchment-lined baking sheet.
In a small bowl, whisk together the egg and milk. Brush the egg wash on each of the rectangles. Spoon a heaping tablespoon of filling into the center of each rectangle, leaving ½" of space around the edge.
Take out the second piece of dough and roll out to the same size as the first. One at a time, place a second rectangle on top of the 9 assembled ones. Use your fingers to press around the seems and then use a fork to form the edges. Poke holes in the tops of each filled pastry to allow steam to escape. Brush with egg wash. Place the pop tarts in the fridge for 30 minutes.
Preheat oven to 400°F. Bake the pop tarts for 15-20 minutes or until lightly browned, rotating halfway through. Let the pop tarts cool on the pan for 5 minutes before transferring to a wire rack to cool completely before glazing.
Whisk all of the ingredients in a medium bowl until it reaches spreading consistency. You want a thick glaze that is easy enough to spread. Spread over the top of each pop tart. Allow the icing to cool for 15 minutes so the frosting can set.