For the marshmallows, place the granulated sugar, glucose and 200ml/7fl oz of water into a heavy-bottomed saucepan and bring to the boil.
Cook over a medium high heat until a sugar thermometer shows 127C/260F.
Place the egg whites into a clean grease-free bowl and whisk to firm peaks.
Add the soaked gelatine sheets and water to the hot sugar syrup very carefully. Stir through, then pour into a jug.
Continue to whisk the egg whites, then pour the sugar syrup onto the egg whites, whisking all the time until the whites are shiny.
Add the vanilla extract and continue to whisk for about 5-10 minutes, or until the mixture is thick enough to hold its shape on a whisk.
Lightly oil a shallow 30x20cm/12x8in baking tray.
Dust the tray with some icing sugar and cornflour, then spoon the mixture into the tray, smoothing the top with a wet palette knife.
Place in the fridge for at least one hour to set.
Dust some more icing sugar and cornflour over the work surface.
Loosen the edge of the marshmallow, then turn out onto the dusted work surface.
Cut into squares and roll in the icing sugar and cornflour to coat totally. Carefully place the marshmallows onto a skewer.
Either place on a hot griddle, under a grill, over an open fire or into a tandoor and grill for 1-2 minutes, or until slightly charred and gooey.
For the chocolate sauce, place the sugar and 110ml/4fl oz water into a saucepan and bring to a simmer.
Cook for 1-2 minutes, or until all the sugar has dissolved, then add the chocolate.
Whisk until smooth and then remove from the heat.
Serve the marshmallows with the chocolate sauce in a bowl on the side.