Prepare pan: line a 9x13 Jelly Pan with parchment paper (not wax paper, this will melt) and coat the parchment paper with softened butter to ensure the caramels will easily release once cooled.
In a large heavy bottom sauce pan/pot on medium heat- melt butter.
In a medium bowl- combine sugar, salt, corn syrup and sweetened condensed milk
Once the butter is fully melted, combine remaining ingredients in the large pot on the stove. Turn heat up to medium-high until mixture begins to boil (10-15 minutes).
Once the mixture begins to boil, turn the temperature down to medium, add the candy thermometer and set to Firm Ball Stage (248 ° F) and stir constantly. This can take 20-30 minutes.
Once the mixture has reached 245 to 248 ° F and become thick and paste like and is a deep dark caramel color, remove from the heat and stir in the vanilla. Careful as it will bubble rapidly during this step.
Immediately pour the caramel into the prepared pan to cool. After 20-30 minutes of cooling, sprinkle the finishing sea salt all over the caramel.
Allow to cool overnight to completely firm up. Carefully pull the parchment paper with the caramels out of the pan and place on a large cutting board. Using a knife or pizza cutter (this works best), cut 1x1 inch squares and wrap in wax candy wrappers.