Grease a 9" springform pan (line the bottom) and preheat the oven to 175°C.
Add the butter and both chocolates to a pan and gently heat until just melted. Add the brewed coffee, stir and set to one side for a short time.
In a large bowl, whisk the eggs and sugars together. Add the melted chocolate/butter mixture and stir until combined.
Combine the flour and cocoa and stir into the wet ingredients just until everything has come together.
Pour into the prepared pan and bake for around 25 minutes. The top will feel very firm but an inserted skewer is not completely clean. When ready, remove from the oven. Wait ten minutes and then remove the springform sides, then allow to cool completely (you may find and hour or two in the fridge will make it easier to slice).