Place the undamaged lids on your jars. Close to “finger tight” (you should be able to easily unscrew with just your fingertips). Drop jars carefully into water. Jars should be completely submerged and you should see small air bubbles escaping the jars.
Let cook for 1 hour. Remove mason jars to a towel on the counter to cool. Once cool to the touch, place in the refrigerator if not serving immediately. If serving immediately, place in an ice bath to continue cooling.
When ready to serve, remove the lids. Spoon turbinado sugar on the top of each custard to create a thin, even layer. Use a small blow torch to caramelize the sugar.