Line 2 baking sheets with lightly buttered aluminum foil. Set aside.

Combine the sugar, corn syrup and water in a heavy 3-quart saucepan. Cook over medium heat, stirring constantly, until the sugar is dissolved. Continue cooking, stirring occasionally, until the mixture reaches the soft crack stage (285*F - 140*C) or when small amount of mixture dropped in cold water separates into hard but not brittle threads.

Add the peanuts and butter. Cook, stirring constantly, to the hard crack stage (300*F - 150*C) or until small amount of mixture dropped in cold water separates into hard, brittle threads. Remove from the heat.

Quickly stir in the baking soda and vanilla (mixture will foam up). Turn the mixture onto prepared baking sheets. Spread out with a metal spatula as thin as possible (warmed pans help to spread mixture thinner).

Cool completely, invert pan and peel off foil; break into serving pieces. Keep in tightly covered container at room temperature.