Spray the pan with oil or coat with softened butter. Cut the parchment to fit into the pan with enough of the paper overhanging to easily pull out the caramels.
Made the Caramel
Combine granulated sugar, butter and corn syrup in a heavy-bottomed sauce pan.
Begin heating over medium heat stirring occasionally until the mixture begins to boil.
If needed, wipe the inside of the pan with a clean brush dipped in cold water to remove any sugar crystals.
Once it begins boiling, slowly begin pouring the sweetened condensed milk into the pot, stirring slowly and constantly. Take your time adding the condensed milk - approximately 2 minutes. The milk needs to be incorporated into the other ingredients slowly.
Place a candy thermometer in the mixture and continue to stir slowly until it reaches 238° F. Note: don't let the caramel boil on its own - you must keep stirring in order to avoid burnt pieces on the bottom. Also, resist the urge to turn the heat to high!
Remove the pan from the heat and stir in the vanilla bean paste (if using).
Cool and Cut Caramel
Pour the caramel into the prepared pan. Optional: sprinkle with sea salt
Allow to cool for 2 - 3 hours. The caramel is ready to remove from the pan and cut once it has fully set.