Dark

What is it?

Swapping the coating changes the balance rather than the structure. Dark chocolate has no milk solids, so it sets harder and snaps more cleanly, which suits a bar already designed around breaking. It also puts bitterness against the wafer for the first time. The filling and the wafer are both sweet and neither brings acidity, so in the milk version there's nothing at all to cut the sugar; the dark coating is the only variant where something does. The four finger format is unchanged underneath, so the groove and the snap work exactly as they do on the milk version. Dark chocolate is also the more stable coating of the two. With no milk solids in it there's less to go stale, which is why a dark bar keeps its snap further into its life.