1. Bring 1½ cups of water, sugar, and corn syrup to the boil over a medium-high heat in a large saucepan. Cook, stirring frequently until the temperature reaches 240 degrees Fahrenheit (115 degrees Celsius) on a candy thermometer. Set aside and keep hot.
2. Mix together the orange juice and orange zest, sprinkle with gelatin, and then set aside.
3. In a small bowl, dissolve the cornstarch in ½ cup cold water, then stir into hot syrup. Place over a low-medium heat, and simmer, stirring gently, until very thick.
4. Remove the syrup from the heat, stir in the orange juice mixture, vanilla and pistachios. Sprinkle an 8x8-inch pan with confectioner’s sugar. Pour the Turkish delight into the pan, and let it cool in a cool, dry place (not the fridge) until set, 3-4 hours.
5. When cool, sprinkle the top with another thick layer of powdered sugar. Cut into 1-inch squares and dredge each one with confectioner’s sugar. Store at room temperature in an airtight container.