Spray a baking sheet with nonstick spray and set aside.
In a small saucepan, combine the sugar, corn syrup and water. Cook on medium-high heat until the sugar melts completely, stirring often with a wooden spoon or heatproof rubber spatula, about 3 minutes.
Turn the heat to medium low and cook until the sugar is lightly golden and reaches 300º, stirring occasionally, about 12 minutes.
Add the butter and peanut butter, stirring as they melt. The mixture will foam up; this is normal. Stir in the baking soda, salt and peanuts, then remove from the heat and pour the mixture onto the prepared baking sheet.
Working quickly before it sets, spread the mixture into an even layer on the sheet, about 8 by 4 inches. Be careful, as the candy will be hot.
Let sit at room temperature until completely hardened, about 1 hour. Break into pieces and serve.