Preheat oven to 200. Pour Chester's Puffcorn into a baking pan or oven safe dish. In a 2 quart saucepan, cook together butter, brown sugar, light corn syrup and vanilla for 2 minutes. Add baking soda to mixture which will cause caramel mixture to foam. Pour caramel mixture over Puffcorn in baking pan and stir until mixed. Place in oven for 45 minutes. Sir every 10-15 minutes. Remove from oven and place on wax paper and break apart.