Heat the cream and chocolate in a saucepan over medium low heat, whisking continuously until chocolate is combined with cream. Set aside to cool.
Whisk the egg yolks with the sugar and salt until well combined.
Temper the egg yolk mixture by pouring a very small amount (⅛ cup) of the chocolate mixture into the egg yolks while whisking quickly. Slowly continuing adding more until the egg yolk and chocolate mixtures are fully combined.
Stir in the instant coffee and vanilla.
Pour the mixture into 10 4-ounce canning jars, filled ¾ full. Place the lids on and tighten fingertip tight.
Using tongs, place the jars into the water bath and cook for 90 minutes.
Remove carefully (they will be hot) and let cool enough to handle.
Wipe any excess water off the inside of the lids and chill in the fridge for at least 3 hours. Serve with whipped cream.
Notes
Add couple sprinkles of Maldon salt to the top before serving for added flavor.
Always let it chill in the fridge for at least 3 hours to allow the custard time to set properly.
Do not overtighten the jars as they could crack under the pressure of the water bath.
When tempering the egg yolk mixture, make sure the be whisking constantly to avoid cooking the yolks at all.