Soak the gelatine leaves in a bowl of cold water for about 5 minutes, until softened. Remove the softened gelatine pulp from the water and squeeze to remove any excess liquid.
In the meantime, pour the sugar, liquid glucose and water into a heavy-based saucepan. Bring to the boil
until the mixture reaches 127°C on a sugar thermometer. Stir in the gelatine along with the lemon and lime zest.
Whisk the egg whites in a spotlessly clean, dry bowl until soft peaks form.
Slowly whisk the hot sugar mixture over the egg whites, then add a few drops of lemon essence. Once all the
sugar has been incorporated, continue to whisk until stiff peaks form and the egg whites become glossy.
Lightly brush a tray with shallow sides all over with the sun flower oil. Mix together a little corn flour and
icing sugar, then dust the tray with the mixture. Spread the marshmallow onto the tray with a spatula, ensuring
it’s evenly distributed and the top is smooth. Leave to set for at least 1 hour at room temperature.
Once the marshmallow is set, turn it out onto a surface dusted with corn flour and icing sugar. Using a dry,
hot knife, cut the slab into 2cm x 2cm cubes. Store in an airtight container for a week or two – if they last that long!