Generously grease a 9x13-inch baking dish or line it with parchment paper for easy removal. Set aside while preparing the candy.

In a heavy-bottomed saucepan over medium heat, combine the granulated sugar, milk, corn syrup, and butter. Stir regularly until the mixture comes to a boil and the sugar is fully dissolved.

Clip a candy thermometer to the side of the saucepan. Continue cooking the boiling mixture, stirring occasionally, until it reaches the soft-ball stage, measured at 236°F. This process generally takes between 15 and 20 minutes.

Once the desired temperature is reached, immediately remove the pan from the heat. Stir in the vanilla extract thoroughly, then gently fold in the chopped nuts until evenly incorporated.

Carefully pour the hot candy mixture into the prepared baking dish. Use a spatula to spread it smoothly into an even layer.

Let the candy cool undisturbed at room temperature for about 1 hour, or until fully set. Once firm, slice into squares or bars using a sharp knife.