In a medium-sized saucepan, combine the granulated sugar, corn syrup, and water. Stir the mixture gently over medium heat until the sugar is fully dissolved, ensuring there are no granules left.
Once the sugar has dissolved, increase the heat to high and bring the mixture to a boil. Do not stir at this point; simply allow it to boil until a candy thermometer registers 300°F, which indicates that it has reached the hard crack stage.
After reaching the desired temperature, carefully remove the saucepan from the heat and let it cool for about 5 minutes. Gently stir in the vanilla extract. If you wish to create a colorful swirling effect, add a few drops of your chosen food coloring, being careful not to overmix.
Prepare a baking sheet by lining it with parchment paper. Once ready, pour the hot candy mixture onto the parchment and use a spatula to spread it out evenly, aiming for a thickness of about 1/4 inch.
Before the candy sets completely, sprinkle the chopped nuts and colorful candy sprinkles generously over the surface. With the spatula, gently press them into the warm candy to ensure they adhere.
Allow the rock candy to cool and harden at room temperature for approximately 30 minutes. Once completely set, break it into desired pieces for serving.
Store any remaining rock candy in an airtight container at room temperature. Indulge in this sweet delight throughout the festive season!
Notes
Consider wrapping individual pieces in festive cellophane and tying them with a ribbon for a charming holiday gift.