Preheat oven to 180°C and line a 12-hole 2-tablespoon capacity flat-based patty pan with paper cases.
Using an electric mixer, cream the butter and sugar until it is pale and creamy; add the vanilla essence and the egg and beat until the ingredients are well-combined.
Transfer the mixture to a larger bowl and fold in half the flour and then half the milk/buttermilk; repeat with the remaining flour and milk/buttermilk and stir until the batter is smooth.
Finely chop 1 chocolate bar and stir into the batter. Three-quarters fill each paper case with batter.
Bake for 15-20 minutes or until a skewer inserted into the centre of one of the cupcakes comes out clean; stand the cupcakes in the pan for 10 minutes and then transfer them to a wire rack to cool.
Making the chocolate icing: Combine the chocolate and cream in a heatproof, microwave-safe bowl and microwave, uncovered, on high for 1-2 minutes, stirring every half minute or so with a metal spoon, until smooth.
Spread icing on the cupcakes: Roughly chop the remaining chocolate bar and sprinkle the chocolate honeycomb mixture over the cupcakes (see Notes below).
Notes: (1) Violet Crumble bars are honeycomb covered with chocolate. I don't know if they are available outside of Australia. For English chefs, they are similar to Crunchie Bars. (2) Sprinkle the chopped chocolate bar over the cupcakes just prior to serving as once it is exposed to the air, honeycomb can become sticky.