2. In a heavy 2 quart saucepan, over medium heat, bring to a boil sugar, corn syrup, salt, and water. Stir until sugar is dissolved. Stir in peanuts. Set candy thermometer in place, and continue cooking. Stir frequently until temperature reaches 300 degrees F (150 degrees C), or until a small amount of mixture dropped into very cold water separates into hard and brittle threads. Watch your mixture closely as this can happen very quickly.
3. Remove from heat; immediately stir in butter and baking soda; pour in once onto cookie sheet. The baking soda will cause the mixture to expand considerably. With 2 forks, lift and pull peanut mixture into rectangle about 14×12 inches. Be very cautious because it will be extremely hot. Cool for at least an hour. This can be accelerated by putting the cookie sheet in the freezer. Snap candy into pieces.