Bring 1 1/2 cups water, sugar, and corn syrup to a boil over medium-high heat in a large saucepan. Cook, stirring frequently, until the temperature reaches 240 degrees F (115 degrees C) on a candy thermometer. Set aside and keep hot.
Stir together orange juice and orange zest, sprinkle with gelatin, and set aside. In a small bowl, dissolve cornstarch in 1/2 cup cold water, then stir into hot syrup.
Place over medium-low heat, and simmer, stirring gently, until very thick.
Remove syrup from heat, stir in orange juice mixture, vanilla, and pistachios.
Sprinkle a 8x8-inch pan generously with confectioners' sugar.
Pour the Turkish delight into the pan, 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 powdered sugar.
Cut into 1-inch squares, and dredge each well with confectioners' sugar. Store at room temperature in an airtight container.
