Line a baking sheet with parchment paper or a silicone baking mat.
Pour the sugar, water, and corn syrup into a large saucepan, and set over medium heat.
Cook the mixture, stirring from time to time, until it reaches 245°F. On my gas stove over medium heat, this took just over 20 minutes.
Mix in the peanuts, salt if the peanuts are unsalted, and the butter. Continue cooking and stir now and then until the mixture reaches 300°F. This took about another 8 to 9 minutes on my gas stove at medium heat, so watch closely during the last 20°F since it rises quickly.
Take the pan off the heat and right away, carefully stir in the vanilla extract and baking soda. The mixture will foam up slightly as you mix.
Right away, pour the mixture onto the prepared baking sheet. Use a butter knife, spoon, or offset spatula to gently spread it into an even layer.
Let cool completely, about one hour, then break into pieces.
