Chop the bittersweet chocolate finely and place in a heatproof bowl. Heat the heavy cream and whole milk in a saucepan over medium heat until it just begins to simmer, about 3-4 minutes. Pour the hot cream mixture over the chocolate and let sit for 1 minute, then whisk until completely smooth.
6 oz bittersweet chocolate, 1 cup heavy cream, 0.5 cup whole milk
In a separate bowl, whisk the egg yolks and granulated sugar together until pale yellow and slightly thickened, about 2 minutes. This aerates the yolks and dissolves the sugar.
5 large egg yolks, 0.25 cup granulated sugar
Slowly pour about ¼ cup of the warm chocolate mixture into the egg yolks while whisking constantly. Gradually add the remaining chocolate mixture in a slow stream, whisking continuously to prevent the eggs from scrambling. Stir in the vanilla extract and a pinch of salt.
6 oz bittersweet chocolate, 5 large egg yolks, 1 tsp vanilla extract, pinch salt
Pour the custard through a fine-mesh sieve into a clean bowl to remove any lumps or air bubbles. Divide the mixture evenly among six 4-6 oz ramekins. Place the ramekins in a deep baking dish.
Fill the baking dish with hot tap water until it reaches halfway up the sides of the ramekins. Bake the custards at 325°F (163°C) for 35-40 minutes until the edges are set but the centers jiggle slightly when shaken gently.
Remove the ramekins from the water bath and let them cool to room temperature. Cover the ramekins and chill in the refrigerator for at least 4 hours or overnight to allow the custard to fully set and develop its flavor.
