In a heavy 5-quart saucepan with lid, combine sugar, corn syrup, and water. Cover pot, and bring to a boil over high heat, about 5 minutes. Dissolve sugar by carefully swirling pot often over burner. Keeping lid on will prevent sugar crystals from forming; however, should crystals form, wash down sides of pot with a wet pastry brush.

Once steam just begins to escape from pot, remove cover and reduce heat to medium. Insert candy thermometer, and continue to boil until temperature reaches 230 degrees (thread stage), about 1 minute.

Add peanuts, stirring constantly with a metal spoon until mixture reaches 300 degrees (hard crack stage) and is a rich golden brown, 13 to 18 minutes.

Immediately remove from heat, and quickly add butter, vanilla, and baking soda. Stir with a metal spoon until butter melts; mixture will become foamy. Pour half of mixture down center of each pan, spreading evenly with a spatula. Allow to cool for at least 1 hour.