Pre-heat the oven to 170°C (325ºF) and prepare two small springform pans (mine are 18cm / 7").
Slowly heat the chocolate, Nutella, and butter in a pan until just melted then add in the coffee (or milk)
In a large bowl, whisk sugars together with the eggs, then add in the cooled chocolate mixture.
Sift the flour and cocoa and stir into the wet ingredients until just combined.
Divide the batter evenly between the two pans.
Bake for around 25 minutes, just until the cakes are firm to the touch and cooked through.
Remove from the oven. Let the cakes rest for 10 minutes in the tins, then turn them out onto a wire rack and allow to cool completely.