Preheat oven to 325°F (160°C). Place 6 standard ramekins (6-ounce capacity) in a deep baking dish or roasting pan. Bring a kettle of water to a boil, then set aside.
Place the chopped chocolate in a medium heatproof bowl. In a medium saucepan, heat the cream and milk over medium heat until it just begins to steam and tiny bubbles form around the edges, about 5 minutes. Do not let it boil.
Pour the hot cream mixture over the chocolate and let stand for 1 minute, then whisk gently until completely smooth and glossy. Set aside to cool slightly, about 5 minutes.
In a separate large bowl, whisk together the egg yolks, 1/3 cup granulated sugar, vanilla extract, and salt until smooth and pale yellow, about 1 minute. Do not overbeat or create too many bubbles.
Slowly pour the chocolate cream mixture into the egg mixture in a thin stream, whisking constantly to temper the eggs and prevent scrambling. Pour the combined custard through a fine-mesh sieve into a large measuring cup or bowl with a spout for easy pouring.
Divide the custard evenly among the prepared ramekins, filling each about three-quarters full. Carefully place the baking dish on the center oven rack, then pour the hot water from the kettle into the baking dish until it reaches halfway up the sides of the ramekins.
Bake for 35-40 minutes, until the edges are set but the centers still jiggle slightly when gently shaken. The custard should look glossy and smooth on top.
Carefully remove the baking dish from the oven and let the ramekins sit in the water bath for 10 minutes. Then transfer ramekins to a wire rack to cool to room temperature, about 1 hour.
Cover each ramekin tightly with plastic wrap and refrigerate for at least 4 hours or overnight until fully chilled and set.
Just before serving, remove custards from the refrigerator and blot any condensation from the tops with a paper towel. Sprinkle 1 tablespoon of superfine sugar evenly over each custard. Using a kitchen torch, caramelize the sugar by moving the flame in circular motions until golden brown and bubbling. Let the sugar harden for 1-2 minutes before serving.
