Boil granulated sugar, glucose, and 200ml water in a heavy saucepan.
Cook over medium-high heat until the sugar thermometer reaches 127°C.
Whisk egg whites in a clean bowl until firm peaks form.
Carefully stir soaked gelatine and its soaking water into the hot syrup.
Pour the sugar syrup into the egg whites while whisking continuously until shiny.
Add vanilla and whisk for 5 to 10 minutes until thick.
Lightly oil a 30x20cm baking tray.
Dust the tray with icing sugar and cornflour, then spread the mixture inside.
Chill in the fridge for at least one hour to set.
Dust a work surface with icing sugar and cornflour.
Turn the marshmallow out onto the dusted surface.
Cut into squares, coat in sugar mixture, and thread onto skewers.
Grill or griddle the marshmallows for 1 to 2 minutes until gooey.
Simmer caster sugar and 110ml water in a saucepan.
Simmer for 2 minutes then whisk in the dark chocolate until smooth.
Remove the chocolate sauce from the heat.
Serve toasted marshmallows immediately with the warm chocolate sauce.