Preheat the oven to 175°C (350℉).
Grease or line a small springform pan (18cm / 7") for easy release.
In a pan, melt the butter and chocolate together.
Add the coffee (or milk) and stir to combine.
In a separate bowl, beat the eggs, then whisk in both sugars.
Stir in the cocoa and flour.
Pour into the prepared pan and bake for 18–25 minutes, depending on how gooey you’d like the centre (see note 2).
Let the cake cool in the tin. It will firm up as it cools, but the centre should remain soft.
Dust with icing sugar before serving. Top with blueberries if you like. Please find more serving suggestions.