Instructions for 1000 watt microwave. Lightly grease a standard baking sheet, or cover with parchment paper or use a silicone baking mat.
In a large microwave safe bowl stir together the sugar, corn syrup and salt. Microwave on high for 4 minutes or until bubbly and the sugar dissolves. Stop and stir at 2 minutes, halfway through cooking.
After cooking for 4 minutes total, add the peanuts. Stir until coated.
Return to the microwave cooking for an additional 3 minutes stopping to stir halfway.
After cooking the peanuts in the syrup for 3 minutes, add cubed butter. Stir and return to the microwave, cooking for 1 minute.
Remove from microwave. While stirring, add the vanilla and baking soda. The mixture will foam continue to stir until it does down slightly.
Quickly pour onto the prepared pan or silicon mat and spread to approximately 1/4-inch thickness. You may use an offset spatula spritzed lightly with cooking spray.
Allow to cool completely then break into desired size pieces. Store in an airtight container at room temperature. (Makes about 1 1/2 lbs)