Line a baking sheet with parchment paper.
Mix together the water, sugar, and corn syrup in a 2-quart saucepan until all of the sugar is wet. If sugar crystals cling to the sides of the pan, dissolve them away with a wet pastry brush.
Bring the mixture to a boil over medium-high heat, stirring occasionally and gently with a heatproof spatula until all of the sugar is dissolved. Then boil to 250F without stirring.
Add the peanuts and the butter, stirring constantly and gently, until the mixture reaches 320F.
Remove from the heat, and stir in the salt, vanilla extract, and baking soda until thoroughly incorporated.
Pour the mixture onto the parchment paper, and spread evenly with an offset spatula.
Let cool completely, about 30 minutes. Break into pieces, and store in an airtight container.