In a heavy saucepan, combine the sugar, corn syrup, and water. Cook over medium heat, stirring until the sugar dissolves.
Continue to cook, without stirring, until the mixture reaches 300°F (149°C) on a candy thermometer, or until a small amount of the mixture dropped into cold water separates into hard, brittle threads.
Stir in the peanuts and continue to cook until the peanuts are lightly browned, about 2-3 minutes.
Remove from heat and quickly stir in the butter, baking soda, and vanilla extract. The mixture will foam up.
Immediately pour the mixture onto a buttered baking sheet or silicone mat. Spread thinly with a spatula.
Let cool completely before breaking into pieces.
Notes
Store in an airtight container at room temperature.