Fill a heavy duty pot or sous vide container with water and set the sous vide cooker to 82ºC/180ºF. Cover and place the mason jars or ramekins on top. This will warm the jars and lessen instances of cracking, I've found.
Place the chocolate in medium bowl and set aside.
Add the egg yolks, sugar, water, espresso, vanilla and salt to a medium bowl and whisk to combine. Set aside.
Add the milk and cream to a small saucepan and bring to a simmer. Once heated, pour slowly into the egg yolk mixture, while whisking constantly.
While still warm, pour the mixture through a strainer over the chocolate and allow to sit for a few minutes. Stir with a whisk to fully combine.
Add to the warmed jars, filling to within half inch from the top of the jar. Add the lids, ensuring not to tighten too much. Submerge in the heated water using tongs and cook for 45 minutes. Prepare an ice bath a few minutes before the cook ends.
When time is up, remove the jars using tongs and allow to cool at room temperature for 10-15 minutes. Add the jars to the ice bath and allow to cool before refrigerating for 2-4 hours.
Whip up the meringue:
Ensure the bowl and whisks are grease-free. I wipe each with paper towel and lemon or white vinegar, rinse with warm water and dry with a clean towel.
Add the egg whites and sugar to the clean bowl and whisk to combine with a hand whisk. Place the bowl over a pot with simmering water, but don't allow the bowl to come in contact with the water. Whisk constantly until the sugar melts and the mixture reaches 79ºC.
Remove from heat and use an electric mixer to whip the meringue until stiff peaks form. Use immediately.
Assemble and serve:
Remove the jars from the refrigerator about 10 minutes before serving and spoon some meringue on top. Use a fork to primp and peak the meringue. Use a hand torch to lightly toast.
Notes
Without the meringue, these will last for about a week in the refrigerator.