Preheat oven to 160ºC (320ºF). To make the cocoa snaps, place the butter, sugar and glucose syrup in a saucepan over low heat and stir until the butter is melted and the sugar is dissolved. Add the flour and cocoa and stir until well combined. Set aside for 15 minutes to cool. Roll ½ teaspoonfuls into 10cm lengths. Place on baking trays lined with non-stick baking paper, leaving room to spread. Cook for 8–10 minutes or until bubbly and spread. Allow to cool on the trays.
Place the chocolate in a heatproof bowl over a saucepan of simmering water and stir until melted and smooth. Pour into a large bowl and set aside. Place the eggwhites in a bowl and whisk until soft peaks form. Gradually add the sugar and whisk until thick and glossy. Place the cream in a bowl and whisk until stiff peaks form. Gradually fold the eggwhite mixture through the chocolate. Fold through the cream. Cover and refrigerate for 2 hours or until set. Spoon the mousse onto half of the cocoa snaps and sandwich with remaining snaps. Makes 14.
+ Glucose syrup is available from the baking aisle of most supermarkets and in health food shops.