Combine the cream and milk in a small saucepan. Bring to a simmer and remove from heat. Add the hibiscus and stir. Cover and let stand for 10 minutes.
Melt the chocolate in a double boiler, or in a heat-proof bowl set over a pan of simmering water, stirring from time to time to dissolve. Let cool slightly.
In a medium mixing bowl, whisk together the sugar and egg yolks. Add the chocolate and blend well. Pour the cream into the bowl through a fine-mesh sieve and discard the hibiscus. Blend well.
Pour into four 6-ounce ramekins, preferable wide and shallow, and place in a baking dish large enough to accommodate them. Pour very hot water into the dish to reach half the height of the ramekins (this prevents the custard from boiling).
Bake for 45 minutes, until the custard is set but still slightly wobbly in the centre. Let rest in the baking dish on the counter for 15 minutes before removing the ramekins (caution: they will still be hot). Let cool to room temperature, cover with plastic wrap, and chill for 2 hours, or up to a day. Remove from the fridge 30 minutes before serving.
Just before serving, sprinkle turbinado sugar over the surface of the custard. Place the ramekins on a non-flammable surface (your cooking range, for instance) and away from anything flammable. Use a blowtorch to melt and caramelise the sugar: be very cautious, follow the manufacturer's instructions if any, and keep the nozzle away from you or anyone you care about. Move the torch slowly over the sugar at a height of about 3 inches, moving it constantly to ensure an even caramelisation. (Alternatively, you can put the ramekins in the oven under a very hot broiler for 2 minutes: the sugar won't melt as thoroughly, but it will form a slight crust nonetheless.) Let cool for a minute and serve.