Method:

Preheat the oven to 170C and prepare a cupcake tin with liners.
In a bowl combine the flour, sugar and bicarb.
In a separate bowl combine the egg, buttermilk and vanilla essence.
In saucepan combine the margarine, oil, water and cocoa and bring to a gentle simmer.
Add the buttermilk mixture to the flour mixture and combine.
Add the oil mixture the batter and mix until smooth. Pour the batter into the cupcake liners and bake for 20 minutes.
In the meantime, make the icing by whisking the butter until fluffy. Add the cocoa, icing sugar and essence and whisk until combine. Transfer into a piping bag fitted with a star nozzle.
Remove the cupcakes from the oven, allow to cool completely.
Pipe the buttercream over the cupcakes and top with the peppermint crisp shards.