Spread popcorn in a large baking pan. Preheat oven to 300F. For caramel mixture, in a medium saucepan combine the brown sugar, butter, corn syrup and add 1/4 tsp salt if you wish (I never do because the butter I use is salted). Cook and stir over medium heat until mixture boils. Continue to cook 5 minutes. Remove from heat and pour over popcorn. Toss quickly to coat. bake for 15 minutes and then stir. Return to oven and bake an additional 5 to 10 minutes until well coated. Turn popcorn out onto foil to cool. Break into pieces and serve. Stores well in zip-lock bags.