Line a 15 x 30cm rectangular pan with wax paper.
Combine sugar and ⅔ cup hot water in a saucepan over medium heat.
Cook, stirring, for 3 minutes or until sugar dissolves and syrup is clear.
Using a fork, combine gelatine and ⅔ cup cold water in a small jug then add to the hot syrup.
Cook, stirring, for 2 to 3 minutes or until gelatine has dissolved and mixture is clear.
Pour into the bowl of an electric mixer.
Set aside to cool to room temperature (about 30 to 40 minutes).
Using electric mixer, beat on high for 8 minutes or until very thick.
Add rosewater and beat for 2 minutes.
Pour into prepared pan. Smooth surface using a spatula.
Refrigerate for at least 1 hour or until set.
Lift onto a board. Using a hot knife, cut the marshmallow into 24 squares.
Toss in coconut to serve.