Place butter, chocolate, cream, water and espresso in a saucepan and melt well.
Once everything has melted, add the sugar and stir until it is well dissolved.
Wait for the mixture to reach room temperature and then add the eggs, little by little, with a whisk or with the help of a planetary mixer.
Gradually add the flour, cocoa, baking powder and salt and mix well with the whisk until the mixture is smooth and homogeneous.