This is a tried-and-true recipe from my grandmother, Zelda (aka "Grammy"). She was THE cook of the family. She taught me to make this when I was 8 years old. She SWORE it worked best made in a cast-iron skillet...so that's how I make it. Who am I to deviate from perfection?
NOTE* It's important to use RAW peanuts...they cook in the sugar. If you use peanuts that have already been roasted, you run the risk of burning them.
In CAST IRON SKILLET, cook sugar, corn syrup and peanuts while stirring CONSTANTLY until amber color.
Add butter, stir well.
Remove from heat, stir in baking soda and IMMEDIATELY pour onto greased foil. QUICKLY spread with knife as this stuff sets up fast. Let cool COMPLETELY. Break into pieces and store in air-tight container.