200 g (7 oz) plain dark chocolate, broken into small pieces
4 eggs, separated
150 ml (1/4 pint) double cream
sunflower oil, for greasing
5 tablespoons granulated sugar
2 tablespoons golden syrup
1 teaspoon bicarbonate of soda
To make the honeycomb, oil a baking sheet and set on a chopping board. Gently heat the sugar and golden syrup in a heavy-based saucepan until the sugar has dissolved, then boil until the mixture turns a deep golden caramel. Whisk in the bicarbonate of soda (this will make it foam up), then quickly pour it on to the prepared baking sheet and leave to cool for 10 minutes.
Meanwhile, melt the chocolate in a heatproof bowl set over a saucepan of gently simmering water. Leave to cool slightly, then stir in the egg yolks. Lightly whip the cream in a bowl with a hand-held electric whisk until it forms soft peaks and fold into the chocolate mixture.
Whisk the egg whites in a clean large bowl with a hand-held electric whisk until stiff, then fold into the chocolate cream.
Break the honeycomb into small chunks and fold most of it into the mousse. Pour into 6 glass tumblers or dishes and chill for 10 minutes until set. Sprinkle the leftover honeycomb over the top just before serving.