Preheat the oven to 180°C/160°C fan/350°F and spread the cashew nuts on a baking sheet. Toast the nuts in the oven for 8–10 minutes until light golden brown. Leave to cool slightly, then roughly chop the nuts and set aside for later.,

Combine the butter, icing (confectioners’) sugar, cocoa powder and salt in a large bowl. Beat together until smooth, then add 50ml (1¾fl oz) of the milk and mix to combine. Finally, add the double (heavy) cream and beat for 2–3 minutes until smooth and light.,

Place the remaining milk in a separate, shallow bowl and dunk the Rich Tea biscuits (Graham Crackers) in the milk one at a time for 5 seconds each. Don’t leave them in there any longer, or they will break down and turn soggy. Arrange the soaked biscuits in a layer on the base of a 16cm x 20cm (6¼in x 8in) serving dish or 8 individual ramekins. Once you have a single layer of biscuits, spread a third of the chocolate mixture on top and level the surface with the back of a spoon. Repeat the process, alternating a layer of biscuits and a layer of chocolate buttercream, until you have 3 layers of each. Cover the pudding and refrigerate for 2–3 hours until the buttercream firms up.,

To serve, cut into square portions and sprinkle the roughly chopped cashew nuts on top.