Position rack in middle of oven. Preheat oven to 300° F/150°C. Arrange whatever ramekins you are using in a roasting pan.

Whisk heavy cream and half-and-half together in a saucepan and bring just to a boil over medium heat; remove from heat and whisk in chocolate and vanilla. Whisk until chocolate is melted and mixture is smooth. Set aside and keep warm.

Meanwhile, whisk the egg yolks and 1/3 cup (65 g) sugar in a heatproof mixing bowl. Gradually whisk in a little but of the warm cream mixture, to temper the eggs, then whisk all of the cream into the eggs to combine well.

Pour this mixture through fine sieve into a 4-cup (960 ml) measuring cup with a spout, or a pitcher. Pour the custard into the ramekins, filling them about three-quarters of the way full. Pour hot tap water in the roasting pan to come about halfway up the sides of the ramekins. Transfer very carefully to the oven.

Bake for about 25 to 35 minutes or until the center of the custards jiggle slightly; they should not be completely firm. Remove custards from water, cool a bit at room temperature and then refrigerate for at least 2 hours or up to overnight. If refrigerating overnight, cover with plastic wrap.

Right before serving, sprinkle a thin layer of the raw sugar (or turbinado or white sugar) on top of each custard. Use a propane or butane torch (my choice) to caramelize the chocolate. Alternately, preheat broiler to high and watch very carefully.

PS: some folks like to chill the custards again after caramelizing the sugar. I like to serve them right away.