1. Gently crush the nuts into good sized pieces. Whip the cream using an electric whisk until it forms hard peaks.
2. Separate the whites and the yolk. Add the almond liquor to the egg yolks and pistachio nuts and mix well. Beat the egg whites with an electric whisk, slowly add the sugar in whilst beating. Whip the whites until they can form soft peaks.
3. Mix the yolk mixture into the cream and with an metal spoon gently fold in the egg whites, making sure you do not knock the air out. Roughly crush up half of the biscuits. Add all of the biscuits into the semi-fredo mix.
4. Line a loaf tin with cling film and pour the mixture in. Cover the top with cling film and place in the freezer for 2 to 3 hours. To serve dust with cocoa and slice to serve.