Method

1 Preheat oven to 180°C. Grease a 26 x 16cm (base measurement) slab pan with melted butter, then line with baking paper.
2 Sift flour into a large bowl. Add brown sugar and stir to combine. Add butter and vanilla and mix to combine. Spoon into prepared pan and press evenly over base.
3 Bake for 20 minutes or until light golden. Set aside to cool completely.
4 Meanwhile, put ¼ cup of the water in a microwave-safe jug and sprinkle gelatine over. Set aside for 5 minutes or until softened. Cook in microwave on high/100% for 20-30 seconds or until gelatine is dissolved. Set aside to cool. Put caster sugar and remaining water into the bowl of an electric mixer and beat for
5 minutes or until mixture turns white. Add gelatine mixture and beat for 10 minutes or until a thick white marshmallow forms.
5 Spread marshmallow onto biscuit base, then sprinkle with coconut. Stand for 1 hour or until marshmallow has set. Cut into rectangles using a large wet knife, dipped into hot water between cuts. Serve.