Line a 20cm square baking dish with lightly greased foil or cling wrap. Grease another piece of foil or cling wrap to cover the top, and set aside.
Place 1/2 cup of water in the bowl of an electric mixer and sprinkle gelatine on top of water to soak.
While gelatine is soaking, combine 1/4 cup of water, golden syrup and sugar in a saucepan and bring to a boil over medium heat. Boil the mixture hard for 1 minute.
Pour the hot sugar mixture into the gelatine mixture and beat on high for 12 minutes with electric mixer, until the mixture is fluffy and forms stiff peaks. Add vanilla and peppermint essences, and beat just until blended.
Pour the marshmallow mixture into the prepared baking dish, using a greased spatula to smooth the top. Cover with the reserved greased foil or wrap, and press down lightly to seal the covering to the top of the mix.
Allow the mix to rest for 4 hours or overnight. Mix together cornflour and icing sugar in a shallow dish. Using oiled scissors or an oiled kitchen knife, cut the marshmallow into strips, then into 3cm squares. Coat the marshmallows lightly with cornflour and store in an airtight container.