Ultimate S'mores are puff pastries filled with milk chocolate and marshmallow fluff, baked in the oven, and topped with a dusting of graham cracker crumbs, cinnamon, sugar, and chocolate.
Preheat the oven to 400°F and line a large baking sheet with parchment paper.
Lay puff pastries on a flat surface and cut each sheet into 9 squares, for a total of 18 squares between both sheets.
Place nine puff pastry squares on the lined baking sheet. Reserve the other nine.
Divide the chocolate evenly between the nine squares. I placed three sections from the chocolate bars on each of the nine puff pastry squares. (Reserve the 9 remaining chocolate sections for melting and drizzling later.)
Top with about 2 tablespoons of marshmallow fluff.
Using your finger or a pastry brush, wet the edges of the filled puff pastry squares with water and top with the reserved puff pastry squares. Use a fork to crimp and seal the edges.
Use a pastry brush to brush the beaten egg on the outside edges of the pastry.
Meanwhile, in a small bowl, combine cinnamon, sugar, and crushed graham cracker. Set aside.
After the s'mores are done baking, working one at a time, brush the pastry with the melted butter, and then sprinkle the graham cracker mixture on top. (Be sure to work one at a time or the butter will seep into the pastry, resulting in the graham cracker topping not sticking.) Repeat with the remaining pastries.
Finally, melt the remaining pieces of chocolate in a piping bag or zipped plastic bag in the microwave in 15-second increments until liquid.
Cut off the tip of the bag (or corner of the plastic bag) and drizzle the melted chocolate over the pastries. Serve warm.