Choose two small jars or ramekins for the dessert. The dishes need to be oven safe and need to be able to hold ¾ cup liquid.
Preheat oven to 300°F and place a baking dish (such as a loaf pan) in the oven with enough hot water to mostly come up the sides of whatever sized dish you’ll be serving the dessert in.
In a small saucepan, heat heavy cream, milk and sugar until the mixture is hot (but not boiling) and the sugar has dissolved.
Turn off the heat under the pan and add chopped chocolate to the hot milk mixture. Allow chocolate to sit in the hot milk undisturbed about a minute, then stir to combine and until fully melted. Add salt and vanilla.
In a small bowl, add egg yolks and whisk (or stir with a fork). Add a tablespoon of the hot chocolate mixture to the egg and stir well. Continue adding a tablespoon or so at a time until you’ve added at least 5-6 tablespoons and the egg mixture is warm. Add entire egg mixture to the saucepan and turn the stove back on to medium-low.
Heat, while slowly whisking and cook for 2-3 minutes or until the mixture has thickened to almost the consistency of pudding. Immediately remove from heat and pour into your two jars or ramekins.
Retrieve the pan of hot water from the oven, place jars in the center and return to the oven to bake for 20-25 minutes.
Remove desserts from the oven when the edges of the dessert are set, but the center is still quite soft (the center should jiggle a bit, but not appear fully liquid).
Cool desserts on a cooling rack for 15 minutes or more, and then move to the refrigerator to chill and firm up, at least 2-3 hours.
Serve well chilled. Desserts may be made up to 2 days in advance. Cover dishes in the refrigerator if chilling overnight.