To make the marshmallow, using canola oil spray or brush with vegetable oil, to grease and line a lamington tin. Add baking paper and grease the top of the baking paper as well. 

Add the cold water to a small bowl, sprinkle the gelatine over the top and stir immediately to combine. Set aside to allow the gelatine to bloom.  

In a medium sized saucepan, combine the sugar and hot water, stir over medium heat until sugar dissolves, bring to the boil. Carefully, so as not to splash, add the gelatine mixture (it is likely it will have solidified, this is okay) and stir gently to dissolve. 

Return to a boil and simmer uncovered, without stirring, for 20 minutes. Brush the sides of the pan with a wet pastry brush if any sugar crystals begin to form. 

Remove from heat and when bubbling has ceased pour in to mixing bowl and allow to cool for 20 minutes. 

Add the vanilla extract and salt and beat with electric mixer on high-speed using a whisk attachment, until the mixture is thick and white, holds its shape and has tripled in size. This will take about 10 to 15 minutes. 

Spread mixture into prepared pan using an oiled spatula or the back of a spoon. Set aside at room temperature to set (do not refrigerate marshmallow as it will become sticky). The marshmallow should be firm after about 2 hours but if possible, leave for up to 6 hours before cutting. 

Mix cornflour and icing sugar together, dust the top of the marshmallow with some of the cornflour mix before cutting with an oiled or dusted knife. Toss each square in the remaining cornflour mix.

To assemble the S’mores, top half the biscuits with a few squares of chocolate before toasting the marshmallows, preferably over an open fire but they can be toasted in the oven. Top the chocolate with a hot, toasted marshmallow and top with another biscuit to serve. 

Store in an airtight container at room temperature for up to two weeks.