Preheat the oven to 180ºc/160ºc fan and line an 8" cake tin with parchment paper
Add the dark chocolate and butter to a bowl and melt - you can do this in the microwave, or in a bowl over a pan of simmering water
Once melted, add in the sugar, vanilla, salt and coffee and mix together until combined
Add the eggs and cocoa powder and mix again until combined
Pour into the tin and bake for 25-30 minutes
Leave to cool in the tin for at least 10 minutes, or cool fully in the tin - just make sure to run a knife around the edge of the tin to stop the cake sticking as it cools
Serve still slightly warm, or cooled
Notes
This recipe is best on the day of baking, but can be kept in the fridge for 3-4+ days once made
You can freeze this cake for 3+ months
I use this 8" cake tin in my bake - but it's quite a shallow cake so a thinner one should be fine
See notes on whipping the eggs for a different texture cake if you want to try that instead
The coffee brings out the flavour of the chocolate and doesn't make the cake taste like coffee