Heat the orange rind and juice and Southern Comfort or sherry gently in a pan with the raisins, prunes and mixed spice for 3–5 minutes until the fruit has plumped up and the liquid has been absorbed. Purée in a food processor.
Beat 125 g (4 oz) sugar and the egg yolks together in a bowl for 5 minutes until thick and creamy. Fold in the cream. Add the blended fruit and chocolate.
Whisk the egg whites in a grease-free bowl until softly peaking. Whisk in the extra 1 tablespoon sugar. Fold the egg whites into the rest of the mixture and gently mix together.
Line a 1 kg (2 lb) loaf tin with clingfilm. Freeze the mixture in the tin for 6 hours. Serve sliced on large plates drizzled with 1 teaspoon Southern Comfort or sherry around each slice.