Combine the sugar, corn syrup, water, and butter in a heavy 4- to 5-quart saucepan.
Cook over medium heat, stirring until the sugar is dissolved.
Then continue cooking without stirring to 230°-234°, or until the syrup spins a 2-inch thread when dropped from a spoon.
Gradually stir in the peanuts so that the mixture continues to boil.
Turn the heat to low and cook, stirring constantly, to 280°.
Remove from heat and stir in the salt, hot water, and vanilla.
Return to medium heat (to give a good golden color) and continue stirring to 300°, or to the hard-crack stage.
Remove from the heat, add the baking soda, and stir just until the mixture foams up well (no longer or it may sugar).
Immediately pour out onto a greased 15 x 10-inch pan.
Spread out as thinly as possible with a greased spatula.
Cool, then break into pieces.
Store in an airtight container.