Melt the chocolate in a thin-sided bowl over a gently simmering bain-marie.
Mix the butter, sugar and salt. Add the eggs one at a time and beat using the whisk on a hand mixer, add the chocolate, continue to whisk until the mixture becomes lighter in colour. Combine the pistachios, flour and baking powder and mix in. Spoon the batter into the prepared muffin tin.
Approx. 25 mins. in the centre of an oven preheated to 180°C. Take the cupcakes out of the oven, allow to cool a little, remove from the tin and leave to cool on a rack.
Cream cheese frosting
Cream the butter and icing sugar using the whisk on a hand mixer, stir in the cream cheese and pistachios. Transfer the mixture to a piping bag with a serrated nozzle (approx. 10 mm in diameter) and pipe onto the cupcakes.