Prepare a sous vide water bath set to 176 degrees F (80 degrees C).
Bring heavy cream to a simmer.
Whisk Lily's dark chocolate baking chips, erythritol, vanilla extract, and salt in with cream. Remove from heat.
Whisk in egg yolk one at a time until mixture is smooth.
Transfer mixture to a pourable measuring cup to easily divide mixture.
Divide mixture into six 4-ounce mason jars.
Screw on lids fingertip tight.
Place sealed jars at the bottom of the water bath.
Cook custards for 1 hour.
Remove jars from the water bath using tongs. (They're hot! Watch out!)
Place the jars in the fridge to cool and set for a minimum of 3 hours.
Serve as is or topped with whipped cream and cinnamon.
This recipe contains 26g of erythritol that can be subtracted from the total carb count to provide the net carb content. That means per serving, you can subtract an additional 4.3g net carb. 13-2-4.3 = 6.7 g net carbs per serving.