Combine sugar and corn syrup together in a microwave-safe bowl; heat in microwave for 3 1/2 minutes. Add cashews and heat in microwave for another 3 1/2 minutes. Stir vanilla extract into cashew mixture and heat in microwave for 1 3/4 minutes.
Stir baking soda into cashew mixture and quickly pour onto the prepared baking sheet. Cool brittle to room temperature and break into pieces.