Whisk flour, sugar, salt and cocoa powder in a medium bowl. Take the butter and work it into the flour, until you have walnut sized pieces of butter. In a small jug, whisk 1 egg and the milk together. Pour it into the dough, and knead.
Divide dough in half. If you're not using it immediately, wrap in clingfilm and shape into discs. Put in fridge.
If you had the dough in the fridge, take it out 30 minutes before using. Place on disc on a floured surface and roll out into a rectangle. Repeat with second disc. You want rectangles to be about 23x30cm. Cut each rectangle into thirds, to make rectangles approximately 8x10cm.
Chocolate Fudge
In a small saucepan, add cocoa powder, milk and 68g of the chocolate. Over medium heat, cook for 3-5 minutes, stirring frequently, until the chocolate is melted and it has thickened slightly. Remove from heat, stir in the remaining chocolate, butter, and vanilla. Transfer to the fridge to thicken.
Marshmallow Icing
Mix sugar, vanilla and salt in a medium bowl.
Melt butter and 30ml of water in a small saucepan over medium-high heat. Add the marshmallows and stir until completely melted.
Pour into the sugar mixture, whisking until combined.
Assembly
Lay half of the rectangles on a parchment lined tray. Take the second egg and beat it in a small bowl. Brush the inside of half of the rectangles, this will be the bottom of the pop tart.
Put the chocolate fudge into a ziplock bag or pastry bag, pipe a line of chocolate on each rectangle on the tray. Make sure to keep 1-1.5cm border around the rectangle. Place mini marshmallows/fluff next to chocolate, and sprinkle with graham crackers.
Place the 'top' of the pop tart on each rectangle, use your fingers to press firmly around the rectangle to seal the dough. Using a fork, press the tines all around the edges.
Prick the top of each pop tart with a fork multiple steams. Refrigerate them for 30 minutes.
Preheat oven to 350°F/175°C
Bake for 20-25 minutes. Let them cool completely
Make the icing while the tarts are cooling. Using a spoon to add icing to each pop tart, and decorate with sprinkles.