Thoroughly grease a 28cm x 19cm x 4cm baking tray. Line with tin foil and spray that, too.
Place sugar and water in small saucepan over low heat. Heat stirring until sugar is completely dissolved. Remove from heat and cool for 10 minutes.
Dissolve gelatine powder in hot water, stirring vigorously.
Put sugar syrup and gelatine mix into mixing bowl and mix on high speed until white and thickened - about 4 minutes.
With beaters still running, add rosewater and red colouring until the desired shade of pink is reached.
Pour into prepared tray and allow to cool at room temperature for about 2 hours.
Cut into squares and dredge in crushed pistachios.