01 - Line a 9x9-inch pan with parchment paper, or lightly butter a marble slab for shaping the candy.
02 - In a heavy-bottomed saucepan, combine the granulated sugar, heavy cream, whole milk, unsalted butter, and salt. Stir over medium heat until the butter melts and the mixture is fully blended.
03 - Bring the mixture to a boil, stirring constantly. Reduce the heat and continue cooking without stirring until the mixture reaches 240°F (soft ball stage) on a candy thermometer.
04 - Remove the saucepan from heat. Add the vanilla extract without stirring it in. Set the mixture aside to cool undisturbed to 110°F, approximately 30 to 40 minutes.
05 - Once cooled to 110°F, beat the mixture vigorously with a wooden spoon until it thickens, turns creamy, and loses its glossy sheen, about 8 to 10 minutes.
06 - Quickly pour or spoon the thickened candy onto the prepared pan or slab. Gently shape into logs or squares and allow to set for 20 to 30 minutes.
07 - Cut the set candy into individual pieces and store in an airtight container at room temperature.