This is so easy, but will impress when you say you made them yourself.The only major purchase is good quality peppermint essence. I used Star Kay from Waitrose, about £3.00, but will last for ages. Thank you James Martin.
300g dark chocolate (50% cocoa solids is fine
3 tablespoons of Demerara sugar
1/2 teaspoon of peppermint essence
Melt chocolate in heat proof bowl over pan of barely simmering water. Mix sugar & essence together, mix into chocolate. Pour chocolate on to baking tin lined with baking paper. Spread to thin equal layer. Leave to set, then either cut into rectangles or break into shards.