Line a baking sheet with sides with parchment paper; set aside.
Measure out in individual bowls, the peanuts, baking soda, and vanilla. Set aside.
In a heavy bottom, 3-quart, saucepan, combine sugar, corn syrup, and water. Cook over medium heat, stirring occasionally until it comes to a full boil, 8-12 minutes.
Add butter and continue to cook on medium heat, stirring occasionally, until a candy thermometer reads 305ºF (about 25-30 minutes) or until a small amount of mixture dropped into ice water forms a hard brittle ball. Do not turn the heat up!
Add peanuts and still until well combined. Remove from heat and stir in baking soda and vanilla.
Immediately pour mixture onto the prepared baking sheet; using a rubber spatula, spread mixture evenly to about ¼ inch thick.
Cool completely and break into the desired sizes.
Store in an airtight container in a cool place for up to two weeks!