01 - Line a 9x9-inch baking pan with parchment paper, or lightly butter a marble slab for working the candy.
02 - In a heavy-bottomed saucepan, combine the granulated sugar, heavy cream, whole milk, unsalted butter, and salt. Stir continuously over medium heat until the butter has fully melted and the mixture is well blended.
03 - Bring the mixture to a boil, stirring constantly. Once boiling, reduce the heat and cook 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 until it reaches 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 - Working quickly, pour or spoon the thickened candy onto the prepared pan or slab. Gently shape into logs or squares. Allow to set for 20 to 30 minutes.
07 - Cut the set candy into pieces and store in an airtight container at room temperature.