Place popped popcorn in a large bowl. Lay a piece of wax or parchment paper on the counter. Set aside.
Place butter, brown sugar and corn syrup in a microwave safe bowl. Cook for one minute. Stir and cook two additional minutes for chewy caramel corn. If you like hard caramel corn, cook an additional minute.
Remove from microwave. Stir in vanilla and baking soda.
Pour caramel over popcorn and stir until well coated. Dump onto wax paper and allow to cool. Store in a zip top bag or airtight container.