Place popcorn and peanuts in a large microwave-safe bowl; set aside. In another microwave-safe bowl, combine the brown sugar, butter, corn syrup and salt. Cover and microwave on high for 30-60 seconds; stir. Microwave 1-1/2 minutes longer.
Stir in vanilla and baking soda. Pour over popcorn mixture. Microwave, uncovered, on high for 2 minutes, stirring several times. Spread on greased baking sheets to cool. Store in an airtight container.