Preheat the oven to 180 C / Gas 4. Lightly oil a 18cm (7 in) square tin and line the base with non-stick baking parchment.
Rinse the glace cherries thoroughly, dry well on absorbent kitchen paper and reserve.
Place the nuts on a baking tray and roast in the preheated oven for 10 minutes, or until light golden brown. Leave to cool slightly, then chop roughly and reserve.
Break the chocolate into small pieces and place along with the butter and salt in a heatproof bowl set over a saucepan of gently simmering water. Heat gently, stirring, until melted and smooth. Alternatively, melt in the microwave using 30 second intervals.
Roughly chop the biscuits and cut the cherries in half. Combine with the chocolate mixture and the nuts; stir well. Spoon the mixture into the prepared tin and level the top.
Chill in the fridge for 30 minutes, remove from tin, discard the baking parchment and cut into 14 bars.
Cover lightly, return to the fridge, and keep chilled until ready to serve.
To serve, lightly sprinkle the bars with sifted icing sugar, if using. Store the bars covered in the fridge.