Place popcorn in a large bolw and set aside. TIP: use two large bowls.
In a saucepan, combine brown sugar, butter, corn syrup and salt; brong to a boil over medium heat, stirring constantly.
Boil 5 minutes, stirring occasionally.
Remove from heat.
Stir in vanilla and baking soda; mix well.
Pour over popcorn and stir until well-coated.
Pour into two greased 13 in. x 9 in. x 2 in. baking pans.
Bake uncovered at 250 degrees for 45 minutes, stirring every 15 minutes.
Cool completely.
Store in airtight containers or plastic bags.
