To make the chocolate fudge filling: In a small saucepan, stir together the cocoa powder, milk, and 3/4 cup chocolate chips. Set over medium heat and cook, stirring, for 5-8 minutes, until the chocolate is melted and the sauce has thickened slightly. Remove from heat, stir in the remaining 3/4 cup chocolate chips, the butter, and vanilla until smooth. Transfer to the fridge to cool and thicken, at least 30 minutes.
Meanwhile, make the dough. In a food processor, combine the flour, cocoa powder, sugar, and Star Fine Food’s Agreena Shortening. Pulse until the mix clumps together to forms pea-size balls. Add 1/2 cup cold water, 1 tablespoon at a time until the dough comes together and forms a ball. If the dough feels dry, add 1-2 tablespoons additional water.
Turn the dough out onto a floured surface. Roll out into a 1/8-inch thickness. Cut the dough into rectangles, about 4 x 3 inches. Place a tablespoon of the chilled chocolate fudge on one half of the rectangles, leaving a 1/4 inch border. Brush the edges with the beaten egg. Lay the other half of the dough over the filling and seal the edges by crimping with the back of a fork. Repeat until you've used all the dough, you will have leftover fudge.
Place the pop tarts on parchment-lined baking sheets. Cover the baking sheets and place in the fridge for 1 hour or the freezer for 20 minutes.
Preheat the oven to 400 degrees F. Bake the pop tarts for 15-20 minutes. The pop tarts will still leak a little. Cool completely before frosting.
Once Cooled, Spread Marshmallow flu on Pop Tarts and top with Spinkles.