Line a 12-section muffin tray with paper muffin cases. Put the lightly salted butter, 150 g (5 oz) of the sugar, the eggs, flour, cocoa powder and baking powder in a bowl and beat with a hand-held electric whisk for about a minute until light and creamy. Divide the cake mixture between the paper cases.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 20 minutes or until risen and just firm to the touch. Transfer to a wire rack to cool.
Chop the peanuts finely. Put the remaining sugar in a small saucepan with the water and heat gently until the sugar has dissolved. Bring to the boil and boil rapidly for 4–5 minutes until the syrup has turned pale golden. Dip the base of the pan in cold water to prevent further cooking.
Add 50 ml (2 fl oz) of the cream and the unsalted butter to the syrup and heat very gently, stirring, to make a smooth caramel. Stir in the chopped nuts and leave until cool but not set. Spoon over the cupcakes.
Melt the chocolate with the remaining cream and golden syrup in a small saucepan over a gentle heat. Spoon over the cakes and leave to set.