Preheat the oven to 300°. In a medium saucepan, combine the cream, milk, brown sugar and salt. Cook over moderate heat, stirring, until the sugar melts and small bubbles appear around the rim. Remove from the heat and whisk in the chocolate until melted. Add the vanilla. In a medium bowl, whisk the egg yolks. Gradually whisk in the hot cream mixture, then strain the custard through a fine sieve into a bowl.
Set eight 1/2-cup ramekins in a roasting pan. Pour the custard into the ramekins and add enough hot water to the pan to reach halfway up the sides of the ramekins. Cover with foil and bake for 35 to 40 minutes, or until the crème brûlées are set but still slightly jiggly in the center. Uncover and let cool in the pan. Refrigerate until very cold and firm, at least 5 hours.
Set the ramekins in the freezer for 20 minutes, until icy cold. Preheat the broiler and position a rack 6 inches from the heat. Place 4 of the ramekins in a baking pan and fill it with ice. Sprinkle about 2 teaspoons of granulated sugar evenly over each crème brûlée and broil for about 1 minute, until the tops are caramelized. Remove the crème brûlées from the ice water and refrigerate just until chilled, about 15 minutes. Repeat with the remaining crème brûlées. Alternatively, caramelize the sugar with a propane or brûlée torch. Top the crème brûlées with the caramel corn and serve.