Step 1: Wash and thoroughly dry each apple. It's crucial that apples are completely dry and free of wax for the candy to adhere. Insert a lollipop stick or wooden skewer firmly into the stem end of each apple.
Step 2: Line a baking sheet with parchment paper and lightly spray with cooking spray. Set aside.
Step 3: In a heavy-bottomed saucepan, combine the granulated sugar, light corn syrup, and water. Stir gently to moisten the sugar. Attach a candy thermometer to the side of the pan, ensuring it doesn't touch the bottom.
Step 4: Cook over medium-high heat without stirring. Once the mixture begins to boil, add the white gel food coloring. Continue to cook until the candy thermometer registers 300°F (149°C), or the 'hard crack' stage.
Step 5: Immediately remove the saucepan from the heat and carefully stir in the vanilla extract. The mixture will be very hot.
Step 6: Working quickly, dip one apple at a time into the hot candy mixture. Tilt the pan to completely coat the apple, rotating it to ensure an even layer. Lift the apple, allowing any excess candy to drip off back into the pan.
Step 7: Immediately sprinkle the dipped apple generously with edible white glitter or sanding sugar, rotating it to coat all sides. Place the coated apple on the prepared parchment-lined baking sheet to cool and set.
Step 8: Repeat with the remaining apples. Allow the candy apples to cool completely at room temperature, which will take about 20-30 minutes, until the candy coating is hard and crisp. Serve within 1-2 days for best results.