Caramel Popcorn (Chicago Style)

6 quarts popped popcorn
1 cup butter
2 cups brown sugar
1/2 cup karo syrup
1 tsp salt
1/2 tsp soda
1 tsp vanilla

preheat oven to 250 degress. place popcorn in a large roasting pan that has been coated with non-stick spray. in a heavy pan, melt butter on med. heat. Stir in brown sugar, corn syrup and salt. Bring to a boil stirring constantly. Let boil for 5 minutes without stirring. Remove from heat and stir in soda & vanilla. Gradually pour over popcorn mixing as you go. bake for 1 hour stiring every 15 minutes.