Fill a cambro or large pot with enough water to cover the jars. Using your sous vide/immersion circulator, preheat the water to 185 degrees F.
Spray each of the half pint jars with cooking spray. Set aside.
Put the eggs, half and half, and salt and pepper into a blender. Blend until everything is very well combined into a homogenous mixture.
Pour the egg mixture evenly into the prepared jars.
Distribute the prosciutto, chives, and cheese evenly among the jars. Give them a stir to distribute the add-ins throughout the egg mixture.
Place the lids on the jars to finger tight. That is, tighten the lids well, then unscrew them approximately half a turn.
Place the jars into the preheated water. The jars should rest on the bottom of the cooking container and small bubbles should be escaping from the lids. If the jars float, then the lids are on too tight.
Allow everything to cook for 30 minutes.
Once 30 minutes have elapsed, remove the jars from the water and allow them to cool slightly.
If eating them now, you can dig in. Otherwise, allow them to cool before popping them into the fridge to store for later.