Start by splitting the vanilla bean down the center. Scrape out all the seeds and place in a large bowl. Take the vanilla bean pod and place it in a small pot with the sea salt and heavy cream. If using vanilla extract, don't add it yet to the sea salt and heavy cream.
Heat the heavy cream mixture over the stove until the cream is simmering. Do not boil! Remove from the stove and set aside to cool slightly. Remove the vanilla bean pod. If using vanilla extract, stir it into this mixture now.
In the bowl with the vanilla bean seeds (or an empty bowl if using vanilla extract), add the egg yolks and 1/2 cup superfine sugar. Beat until the mixture is light, about 2-3 minutes. Meanwhile, place 6 cups of water in a large pot and heat to boiling.
Add about 1/4 of the cream mixture into the egg and sugar mixture. Stir until combined, and then pour the remaining heavy cream mixture into the mixture. Stir until combined.
Pour the prepared mixture evenly into the ramekins - use either (6) 4-ounce ramekins, (5) 5-ounce ramekins, or (4) 6-ounce ramekins. Place the ramekins in a metal 9x13-inch baking pan and add boiling water to the pan until the water reaches halfway up the sides of the ramekins.
Bake for 30-35 minutes at 325 degrees F until the centers are barely set (very slight jiggle). Cool completely at room temperature and then refrigerate for 3-4 hours before serving. (These can be refrigerated for 4-5 days before using)
When ready to serve, add the remaining 1/4 cup superfine sugar on top of the custards in equal portions. I find it helpful to use a little more sugar than needed to swirl around on top of the custard to make sure the top is evenly coated with sugar - then just pour the extra sugar onto the next ramekin. Use a kitchen torch to torch the tops until the sugar melts and browns (or even slightly blackens). See Note 1. Top with fresh berries and enjoy immediately.