Soak the gelatine sheets in cold water for 5–10 minutes until soft, then wring out any excess water.
In a small saucepan, heat the crème de menthe over a low heat, then add the soaked gelatine. Remove from the heat and stir with a metal spoon until the gelatine is dissolved. Set aside to cool.
Melt the chopped dark chocolate, then set aside to cool bu