In the work bowl of a food processor, combine the flour, graham cracker crumbs, and salt. Add in the butter and pulse just until the mixture resembles coarse meal, with some larger chunks of butter remaining. Add the ice water and egg and pulse until it just comes together without being wet, sticky, or crumbly. If the dough doesn’t hold together when pinched between your fingers, add another tablespoon of water and pulse. You can also make the dough by hand with a pastry blender.

Shape the dough into a disk and cover wrap with plastic wrap. Chill in the fridge until firm, at least 1 hour or up to 3 days. You can also freeze the dough, well wrapped in plastic, for up to 2 months. Defrost in the fridge overnight.

In a small saucepan, combine the cocoa powder, brown sugar, milk, salt, and chocolate. Set over medium heat and cook, stirring, until the chocolate is melted. Simmer, stirring occasionally, for about 5 minutes or until slightly thickened. Remove from heat and add in the butter, stirring until melted and smooth. Set aside to cool to room temperature. Mixture will thicken as it cools.

Remove the dough from the refrigerator and place between two sheets of parchment paper. Use a rolling pin to roll the dough out into a large rectangle about 1/8-inch thick. Cut the dough into even rectangles. Place 1 tablespoon of chocolate fudge and 1 tablespoon of marshmallow crème on a dough rectangle, leaving a 3/4-inch border. Top with another piece of dough, pressing out any air and using the tine of a fork to seal the edges. Repeat with the remaining dough rectangles and place on a parchment lined baking sheet. Beat the egg with 1 tablespoon of water. Brush all over the tops of the pop tarts. Prick each tart a few times with a skewer or toothpick to allow steam to escape. Chill in the refrigerator for 20 minutes, or until the dough has stiffened slightly.

Preheat the oven to 375°F. Bake for about 20 minutes, or until golden brown and puffed. Transfer to a wire rack to let cool completely.

While the pop tarts are cooling, place the glaze ingredients in a microwave-safe bowl. Microwave for 30 seconds. Stir and continue microwaving in 15-second bursts until melted. Let cool. Spoon the glaze over the cooled pop tarts and let sit for 10 minutes before serving.