In a blender or food processor, combine eggs, cheeses (or other optional dairy like cream), and salt until smooth.
Place your jars on a work surface and push a half-slice of bacon into the bottom of each one.
Divide the egg & cheese mixture evenly among the jars
Attach lids and close to fingertip tightness. This means using only your fingertips to screw on the ring; if they are too tight, the air pressure within will not be able to release and the jars will shatter on the bath.
Once closed, submerge the jars in the water bath and set your timer for 1 hour.
Remove from the bath and eat immediately, or refrigerate after allowing to cool. You can also slide a butter knife around the edge, pushing gently inwards as you do so to loosen the base. Invert jar onto heat-safe surface and either sear with a torch or place under broiler for a few minutes for color.