First, grease your tin well. Add vegetable oil and use clean fingers to evenly coat the tin. I would suggest a 30x20cm rectangular tin. Then dust the tin liberally with cornflour and icing sugar.

Place the gelatine into a large heatproof bowl (ideally the bowl of a stand mixer if you have one). Add the 2 tbsp cold water and mix well. Set aside.

Next, add the glucose syrup and caster sugar to a large saucepan. Pour in 150ml water and place over a medium heat. Stir gently until the sugar has dissolved in the water. Once the mix begins to simmer, stop stirring. Continue to heat over a medium-high heat, gently swirling the pan, until the sugar syrup reaches 115C (use a jam thermometer to check). At this stage the liquid should be clear and bubbling. Handle the pan carefully as it will be extremely hot.

Remove the pan from the heat and very carefully drizzle the sugar syrup into the gelatine whilst whisking with an electric whisk. You will find this easiest if you use a stand mixer fitted with the whisk attachment.

Once all has been added, whisk on medium-high speed for a further 12-14 minutes - or until you have a thick, white meringue-like texture.

Spoon the mixture into the prepared tin and smooth over the top using a spatula or palette knife. Leave to set for at least 2 hours.

Dust a baking tray or board with cornflour and icing sugar. Tip the marshmallows onto the tray. Dust a large sharp knife with icing sugar & cornflour then cut the marshmallow into equal-sized cubes. Then in a bowl, mix together a few spoons of icing sugar and cornflour then toss each marshmallow in the icing sugar & cornflour.