Wash and pat dry mint and remove leaves from stem and set aside. In a small saucepan, bring water to boil, add mint stems and sugar. Reduce heat and simmer for 15 minutes or until two-thirds of liquid is gone. Remove from heat, strain and cool. Pop mint leaves in small bowl and cover with boiling water for 30 seconds. Strain and refresh under cold water, drain and pat dry. In a food processor, blend syrup and leaves together until leaves are broken into very small pieces. In a clean bowl, fold together mint syrup, cream and mascarpone. Once combined, pop into ice-cream machine and churn until it reaches firm stage, about 40 minutes. Scoop into a baking tray lined with baking paper (20x30cm with 4cm-high sides), spreading evenly, and pop into freezer to set. To make chocolate thins, spread melted chocolate evenly on to a sheet of baking paper (about 3mm thick) and pop into fridge. Once ice-cream has set, remove from freezer and cut into 10x6-8cm rectangles and also cut chocolate into same size. Serve each slab of mint ice-cream with two sheets of chocolate.