-
Coat two 12-by-17-inch baking sheets with vegetable spray.
-
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.
-
Turn brittle out of pan, and snap it into shards.