Spray a 12-inch round pizza pan or other similar size baking sheets with vegetable cooking spray; set side.
Mix peanuts, sugar, corn syrup, and salt in a 2-quart Pyrex measuring cup. Microwave on high power, until nuts are fragrant and syrup is bubbly, stirring after 4 minutes, 7 to 8 minutes depending your microwave’s wattage. Stir in butter and vanilla; continue to microwave on high power until nuts are golden brown, 1 minute longer. Stir in baking soda and then immediately pour onto on prepared pan. Working quickly, spread to desired thickness. Let stand until completely cool, about 30 minutes. Break into pieces. (Can be stored in a tin a couple of weeks—if you can make it last that long.)