Combine chocolate and 1/3 cup thickened cream in a small saucepan; stir over low heat until smooth. Dissolve gelatine in the hot water; add to chocolate mixture. Whisk egg yolks into chocolate mixture; transfer mixture to a large bowl. Cool.
Beat egg whites in a small bowl with electric mixer until soft peaks form.
Finely chop one honeycomb bar. Fold whipped cream into chocolate mixture, then fold in egg whites, in two batches. Gently fold in finely chopped honeycomb bar. Divide mousse among four 3/4-cup (180ml) serving glasses. Cover; refrigerate 3 hours or until set.
Just before serving, chop remaining honeycomb bar into shards; serve mousse topped with honeycomb shards.