In a large pot, add the butter, br. sugar, corn syrup and salt.
Once it all melts, give a quick stir and then just leave it until it boils. Boil for 5 minutes.
Remove pot from heat and add the baking soda and vanilla. Stir.
The mixture will start to double in size so watch closely and pour mixture over the popped corn. Stir the mixture thoroughly.
Bake in the oven for 1 hour at 250 degrees. Stirring it every 15 minutes.
Once out of the oven-continue to stir for it hardens quite easily.
I then sprinkle the sea salt over the popcorn and also sprinkled the dark chocolate flakes. Let cool.
You can store in whatever container you have. This is a very large recipe so I usually give some away as gifts-thus using small Christmas cellophane bags.