Pre-heat your oven to 390℉/180℃. Line 12 muffin holes with cupcake/muffin liners.
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. With an electric/stand mixer, go for a solid 3-5minutes so it is totally combined. Add in the eggs, one at a time and mixing in between.
Now, add the melted chocolate slowly and combine once again.
Add the flour and cocoa powder, fold gently into the wet mixture with a rubber spatula or wooden spoon until just combined.
Fill each cup to about 3/4s full, they don't rise much.
Bake 15-18 minutes. While warm, use something like the end of a wooden spoon or tablespoon measure to create deep indents in the centre of each brownie cup. Let cool.
When cool, add as much caramel as you like to each hole in the brownies. That said, try not to fill to the top as the marshmallows will push the caramel out the top!
Top with either a large marshmallow, or cluster of small marshmallows on each. Blast with a blowtorch or toast in the oven for 5 minutes (same temperature as above). See notes if using a blowtorch - muffin liners are prone to catching fire, be cautious and ready to blow out any mini fires. Once your marshmallows are toasted, serve!