• Pre-heat your oven to 390℉/180℃. Line a 12 hole muffin pan 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 for several minutes. 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 lined muffin pan, no need to worry about filling close to the top, they don't rise much at all.
• Bake 20-23 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 Ganache

• Chop the chocolate up into small pieces if using block chocolate (chocolate chips are fine too). Place the chocolate in a heatproof bowl/jug.
• Heat the cream over a medium heat in a small saucepan. Once it has started simmering, pour it over the chocolate. Leave for 2 minutes, then whisk to create a thick, glossy chocolate ganache. Use plastic wrap or similar to cover the ganache and place this in the refrigerator for 2 hours (up to overnight if making ahead).
• At this point, remove the ganache from the refrigerator and whisk on high until fluffy (about 3 minutes - it should have lightened in color a little). Either pipe or spoon this ganache into the brownie cups. Serve when ready!