01 - Line a large baking sheet with parchment paper or a silicone mat. Press a wooden stick firmly into the stem end of each apple until secure.
02 - In a heavy-bottomed saucepan, combine sugar, water, and corn syrup. Stir continuously over medium heat until the sugar completely dissolves and the mixture is clear.
03 - Increase heat to high and bring to a rolling boil. Stop stirring and cook until a candy thermometer reads 300°F. Remove from heat immediately when temperature is reached.
04 - Stir in vanilla extract if using. Quickly add several drops of red, blue, and white gel food colorings. Gently swirl with a wooden skewer just enough to create visible streaks—do not fully incorporate.
05 - Hold an apple by the stick and dip it into the hot syrup, rotating to coat completely. Lift and allow excess syrup to drip off for 2-3 seconds, then place on the prepared baking sheet.
06 - Repeat with remaining apples. Swirl the syrup briefly between each dip to refresh the marbled pattern. Work quickly before the syrup thickens.
07 - Let the apples sit undisturbed at room temperature for 15-20 minutes until the candy shell is completely hard and glossy. Serve immediately or store at room temperature up to 24 hours.