01 - Line a large baking sheet with parchment paper or a silicone mat. Insert a wooden stick firmly into the stem end of each apple, ensuring it's securely anchored.
02 - In a heavy-bottomed saucepan, combine granulated sugar, water, and light corn syrup. Place over medium heat, stirring continuously until all sugar crystals have completely dissolved.
03 - Increase heat to high and bring mixture to a rolling boil without stirring. Attach a candy thermometer and cook until syrup reaches precisely 300°F, the hard crack stage. Remove from heat immediately.
04 - Stir in vanilla extract if desired. Working rapidly, add several drops each of red, blue, and white gel food colorings. Gently swirl with a wooden skewer to create visible streaks—do not fully incorporate for optimal marbling.
05 - Holding apples by the sticks, dip each apple individually into the hot candy syrup. Rotate continuously to ensure even coating while preserving the swirled pattern. Allow excess syrup to drip off for 5-10 seconds.
06 - Place coated apples on the prepared baking sheet. Briefly swirl syrup between dips to maintain marbling effect. Let apples cool completely at room temperature until candy shell is fully hardened, approximately 15 minutes.