Line a large baking sheet with parchment paper. Place the chocolate in a heatproof bowl and set over simmering water. Stir and heat the chocolate until just melted. Remove from the heat and mix in the cashews, cranberries and currants. Drop heaping tablespoonfuls of the mixture on the baking sheet, ensuring they don’t touch. Refrigerate the clusters until set. Store in a tight-sealing container at cool room temperature. If stacking, be sure to layer the clusters between parchment paper.