Preheat the oven to 325°F / 165°C. Set 6 ramekins in a roasting pan.
Put 225g of chopped bittersweet chocolate in a bowl. Warm 1¾ cups of heavy cream, ½ cup of milk, and 1 pinch of salt in a saucepan, pour over the chocolate, and whisk until smooth.
Whisk 6 egg yolks with 2½ tablespoons of sugar, then gradually whisk in the chocolate mixture. Strain and divide among the ramekins.
Pour hot water into the pan to come halfway up the sides of the ramekins, and cover the pan with aluminum foil. Bake for 30-35 minutes, until the edges are set but the centers still wobble slightly.
As soon as they are cool enough to handle, lift the custards out of the water and cool on a wire rack. Serve warm or at room temperature.
