Dough
Place the flour, sugar, salt, and butter into the bowl of a food processor fitted with a metal blade and pulse for 20 seconds, or until the mixture looks like sand. Add the milk and process for 10 seconds. Add the cold water, 2 tablespoons at a time, and process each time for 10 seconds, just until the mixture comes together. Divide in half, wrap each piece in plastic, and flatten. Place in the freezer for 40 minutes, or overnight in the refrigerator.
Apple Filling
Meanwhile, prepare the apple filling. Heat a medium frying pan over medium heat and add the butter and sugar. When the butter has melted, add the apple cubes, cinnamon and nutmeg and stir. Cook for about 5 minutes, stirring often, until the apples are fork tender. Place into a bowl and let cool to room temperature, about 10 minutes.
Assembly
Set one piece of parchment on the counter, sprinkle it with some flour, and place one of the dough halves on top. Sprinkle a little flour on top of the dough and then place the second piece of parchment on top. Roll on top of the parchment to roll the dough until it is about 9 X 16 inches. Lift up the top parchment several times and sprinkle the dough with more flour. Try not to roll the edges too thin.
Cut the dough into either 3 X 4-inch or 2 ½ X 4-inch rectangles, squares, or use cookie cutters, making sure you have pairs of each shape. Re-roll scraps.Use a metal spatula to lift up each pair of dough pieces and place onto a piece of parchment trimmed to fit a cookie sheet. Brush half the shapes with the egg wash. Scoop up a heaping tablespoon of apple filling and place onto the brushed dough pieces, spreading in one layer and leaving a ¼ to 1/3-inch border. If using jam, two teaspoons is usually enough per pop tart.
Place a second piece of the same size of dough on top, stretch a little to cover, and press tightly to seal the edges. Use the tines of a fork to seal the edges and leave decorative lines. Place the cookie sheet with the assembled pop tarts in the freezer for 20 minutes.Preheat oven to 350°F. Use a fork, toothpick or skewer to poke holes in the top dough to let the steam out. Bake for 25-30 minutes, or until the bottom and edges are lightly browned. Let cool on a wire rack.
Glaze
Place the confectioner’s sugar into a medium bowl. Add the vanilla, cinnamon and boiling water, and whisk until smooth. Let sit for at least 5 minutes to thicken up and either drizzle the glaze over the tarts or spread to cover, as desired.
Caramel
To make the caramel, place the sugar and water into a small, heavy-bottomed saucepan. Cook on medium-high heat without stirring. When the sugar starts to color on the edges, stir the mixture, then let cook, stirring occasionally, until it is a uniform amber color. Turn heat to low, remove saucepan from the heat and add the cream. Be careful, as the mixture will bubble up. Add the butter and stir. Return to the heat and cook for one minute, or until the mixture is smooth. Remove from heat and let cool. The caramel can be made 5 days in advance. Store covered at room temperature.
Serve the pop tarts with ice cream and caramel sauce.
If you fill your pop tarts with jam, omit the cinnamon in the glaze to make the pretty white glaze shown here.
