Line a rimmed baking sheet with parchment paper. Set it aside.
In a large, glass microwave-safe bowl, combine the sugar and corn syrup. Microwave on high for 4 to 5 minutes- until there is consistent bubbling.
Stir in the peanuts. Microwave on high for 4 to 5 minutes- just until the mixture turns light brown (not burnt-- watch closely!)
Carefully stir in the butter and the vanilla. Microwave on high for 2 minutes.
Stir in the baking soda. The mixture may foam and bubble-up. Carefully and quickly pour the mixture onto the prepared baking sheet, spreading it out evenly. Place it on a rack to cool for at least 30 minutes.
Use your hands to break up the peanut brittle. Store it in an airtight container at room temperature for up to 2 weeks.