Heat oven to 180C/160C fan/gas 4 and grease a 12-hole silicone muffin or friand mould, then dust with a little flour, and tip out the excess (a metal tray will work too, but line with muffin cases, as the mixture may stick). Put the pistachios in a food processor and blitz until finely chopped but not greasy. Add the remaining cake ingredients and blend again into a creamy mixture. Use 2 spoons to fill each hole of your tray 2/3 full, place on the middle shelf of the oven and bake for 15 mins or until a skewer inserted comes out clean. Leave to cool in the mould for 10 mins, then run a knife around the edge of each cake and turn out onto a wire rack.
Meanwhile, make the icing. Using an electric hand whisk, blend 3 tbsp of the cream cheese with the butter until smooth, then add the remaining cream cheese and icing sugar. Whizz again until creamy, transfer to a piping bag fitted with a small round nozzle, and chill until ready to use.
When the cakes are cool, pipe spikes of icing on top of each one, then sprinkle with chopped pistachios. Can be made ahead – store the un-iced cakes in a sealed container for up to 3 days and chill the icing for 2 days.