1Heat oven to 200ºF. Butter 2 cookie sheets, 15 1/2x12 inches, and keep warm in oven. Mix baking soda, 1 teaspoon water and the vanilla; reserve.
2Mix sugar, 1 cup water and the corn syrup in 3-quart saucepan. Cook over medium heat, stirring occasionally, to 240ºF on candy thermometer or until small amount of syrup dropped into very cold water forms a soft ball that flattens when removed from water.
3Stir in butter and peanuts. Cook, stirring constantly, to 300ºF or until small amount of mixture dropped into very cold water separates into hard, brittle threads. (Watch carefully so mixture does not burn.) Immediately remove from heat. Quickly stir in baking soda mixture until light and foamy.
4Pour half the candy mixture onto each cookie sheet; quickly spread about 1/4 inch thick. Cool completely, at least 1 hour. Break into pieces. Store in covered container.