Bring water, sugar and corn syrup to a boil over medium-high heat in a large saucepan. Cook stirring frequently until the temperature reaches 115 degrees C on a candy thermometer. Set aside and keep hot.
Stir together orange juice and orange zest then sprinkle with gelatine; set aside.
In a small bowl dissolve cornflour in cold water then stir into hot syrup. Place over medium-low heat and simmer stirring gently until very thick.
Remove syrup from heat then stir in orange juice mixture, vanilla and pistachios.
Sprinkle a 30x30cm tray generously with icing sugar.
Pour the Turkish delight into the tray and let cool in a cool, dry place (not the refrigerator) until set; 3 to 4 hours.
When cool sprinkle the top with another thick layer of icing sugar.
Cut into 2cm squares and dust each well with icing sugar.
Store at room temperature in an airtight container.