• Pre-heat your oven to 180℃ Fan/370℉. Line a 12 hole muffin tin with muffin cases.
• In a small bowl, break up the dark chocolate and melt in the microwave in 20 second intervals, stirring in between to make sure it doesn't burn. Alternatively, set up a double boiler. Do this by placing a heatproof bowl over a small pot of simmering water. Add the chocolate to the heatproof bowl and stir until melted. 
• In a large mixing bowl, whisk together melted butter and both sugars. Add in the eggs, one at a time and mixing in between. Add the melted chocolate slowly and combine once again. 
• Add the flour, salt and cocoa powder, fold gently into the wet mixture with a rubber spatula or wooden spoon until just combined. Scoop into the muffin tin holes, they don't rise much at all so use all the batter!
• Bake 20-25 minutes, until no longer wobbly. While still warm, create the indents by using a teaspoon measure, egg cup or end of a wooden spoon. Press into the middle, leaving tall sides. Let cool.

For the Filling

• Add the butter to a saucepan to melt. Once melted, stir in the graham cracker crumbs.
• Scoop 1 tsp amounts of the graham cracker mixture into each brownie cup. Press down to create a small layer using the spoon.
• Scoop 1 tsp of marshmallow fluff on top of the graham cracker layer. Leave it for a few minutes to settle.
• Optional: use a cooking blowtorch to toast the top of the marshmallow fluff. Top with any remaining graham cracker crumbs plus a piece of chocolate!