In a large, glass, measuring cup, combine the sugar, syrup, salt, butter, and vanilla. Microwave on high for 1 minute. Stir and cook for 2 minutes. Add the baking soda and stir well (mixture will foam).
Combine the popcorn and peanuts in a large brown paper bag. Pour the syrup into the bag and stir to coat. Turn the bag under to close and microwave on high for 1 minute.
Transfer the caramel corn mixture to a baking sheet lined with waxed paper to cool. Store in an airtight container until ready to serve.