Line a 20x20cm pan with cling wrap leaving enough overhang to cover the top. Spray cling wrap lightly with cooking spray. Place the 6 tablespoons of warm water in a large bowl and sprinkle gelatine on top. Let gelatine soften in the water for 5 minutes.
Combine the white sugar, golden syrup and 1/4 cup water in a tall saucepan. Bring to a boil, stirring constantly. Boil for one full minute. Pour the hot syrup over the softened gelatine and add the salt. Beat at high speed with an electric mixer until the mixture increases in volume and holds a peak, about 8 to 10 minutes. Stir in the vanilla and peppermint essences.
Pour into prepared pan, add several drops of red food colouring and swirl with a toothpick. Cover lightly with cling wrap and let stand at room temperature for 4 hours. Cut into 16 squares using a knife sprayed with cooking spray.
Combine cornflour and icing sugar in a bowl. Toss cut marshmallows in the icing sugar mixture. Store in airtight container or resealable plastic bag.