Combine King syrup, sugar, butter, and salt in a saucepan. Cook over medium heat until all of the sugar is dissolved. Add the whole bag of blanched peanuts to the mix. Stir constantly until the peanuts become light brown. Remove from heat and quickly stir in baking soda.
Spread on a shallow, greased pan (a cookie sheet with a lip works best). Let it cool to room temperature (about an hour) to give it time to harden. It should be hard and cool to the touch before you break it up. Invert the pan and dump. Crack into smaller pieces using the handle of a butter knife.