Preheat oven to 325F (160C).

Place finely chopped chocolate in a large heatproof bowl and microwave in 20-second intervals, stirring in between, until completely melted and smooth. Set aside.

In a medium saucepan, combine heavy cream, whole milk, and salt. Heat over medium-low heat until steaming.

Remove from heat and, very slowly, while whisking, gradually pour into the melted chocolate, whisking until smooth.

Meanwhile, in a separate dish, combine eggs and sugar and whisk gently until well combined (try not to incorporate too much air or whisk too vigorously, as this could make your pot de crème rise and fall in the oven).

While whisking the eggs, slowly drizzle the chocolate mixture into the egg mixture until combined.

Stir in vanilla extract.

Pour through a fine mesh strainer into a bowl or large measuring cup, then pour evenly into ramekins (each ramekin will need a little less than ⅔ cup of the mixture).

Place ramekins in roasting pan then carefully pour water around the ramekins, filling ⅔ up the sides.

Transfer roasting pan to center rack of oven and bake for 35-40 minutes, until mixture is just set on the edges. It should be a bit jiggly in the center if jostled but should not slosh in the ramekin like liquid. (if using a thermometer, an instant read thermometer inserted in the center of the custard should read 160F/73C)

Carefully remove roasting pan from the oven and allow ramekins to cool in the water for about 15 minutes.

Once slightly cooled, use tongs or a towel to carefully remove from the water and allow to cool completely on a cooling rack at room temperature for 30-60 minutes.

Cover each ramekin with plastic wrap and refrigerate at least 2-3 hours, until completely chilled.