In a small pan, dissolve the gelatine in half the water over moderate heat. It should look clear and runny.
In another heavy pan, dissolve the sugar in the remaining water with the strip of orange peel, stirring with a wooden spoon until dissolved. If crystals form on the side of the pan, brush down with a brush dipped in water. Bring to the boil, remove from the heat and add to the gelatine mixture.
Return to the heat and simmer over low heat for 20 minutes, stirring constantly. Remove from heat, take out the peel and add the rosewater, red food colouring and pistachios. Cover and leave 15 minutes.
Skim off the skin and pour into a lamington tin. Allow to set overnight in the refrigerator.
Cut into squares, and toss the squares in the icing sugar/cornflour mixture.