In a large, heavy stockpot over medium heat, combine the sugar, corn syrup, butter, salt, and cayenne pepper.
Stir until the sugar has dissolved.
Clip on a candy thermometer, stop stirring, and boil until the temperature reaches 300°F.
Immediately remove the pot from the heat.
Sprinkle the baking soda over the syrup and stir.
The contents will bubble vigorously.
Immediately stir in the peanuts.
Quickly pour the mixture onto a sheet pan sprayed with nonstick baking spray.
Try to pour the brittle evenly; you can use a small offset spatula (also sprayed with nonstick spray) to coax the brittle to spread evenly in the pan while it's still warm.
Allow to cool completely and break into pieces.
Store in an airtight container for up to 2 weeks.