2 oz. unsalted butter
1/4 cup light brown sugar
1/8 tsp. sea salt
1/2 vanilla bean
1¾ cups heavy cream
1¾ cups whole milk
6 egg yolks
Sea salt for finish
Preheat the oven to 325°F.
Melt the butter in a large saucepan over medium heat. Whisk in the brown sugar and salt. Split the vanilla bean lengthwise, scrape out the seeds, and add to the mixture. Stir until the sugar has dissolved and the mixture has turned golden brown.
Reduce the heat to medium-low and whisk in the cream. The mixture will bubble up. Continue whisking slowly for about five minutes, until the sugar dissolves and the mixture boils. Remove from the heat and whisk in the milk.
Put the yolks in a large heatproof bowl, and whisk lightly. Slowly whisk in the milk mixture. Using a fine-mesh sieve, strain the custard into a heatproof bowl or large measuring cup with a spout.
Place four 4-ounce ovenproof ramekins in a large roasting pan or baking dish with high sides. Divide the custard among the ramekins. Place the pan in the oven and pour enough hot water into the pan to come halfway up the sides of the ramekins. Lay a sheet of aluminum foil over the pan.
Bake the custards for about 50 minutes, until they are set just around the edges and the centers move slightly when the ramekins are gently shaken. Transfer the ramekins to a wire rack to cool, about one hour. Cover each with plastic wrap and refrigerate until chilled, at least five hours.
When ready to serve, sprinkle sea salt over each pot de crème and serve chilled.