Lightly yet thoroughly brush a marble slab or baking sheet with vegetable oil.

Stir together the sugar, corn syrup, water and salt. Bring to a low boil and cover for three minutes, allowing the steam to cook down any sugar crystals that may have formed on the sides of the pan.

Uncover and boil till a candy thermometer reaches 250°F. ( If sugar crystals form on the sides of the pan, brush them down with a pastry brush dipped in warm water.) Add the peanuts, stir occasionally for even cooking and boil till the thermometer reaches 295°F.

Remove from heat and stir in the baking soda, vanilla and butter-it will foam and possibly sputter, be careful.

Immediately pour the mixture onto the prepared slab or sheet, spreading it wide as you pour. With a flexible metal spatula, spread the mixture as thinly as possible. Let cool for 5 minutes and run the spatula under the candy to prevent sticking.

Allow to cool completely, crack into small pieces and store in an airtight tin for one week. You may need to use the flexible metal spatula to remove the candy from the slab.