Use a whisk to mix the egg yolks, sugar and salt together.
Stir in the cream until a uniform substance is formed. Add the vanilla and mix to combine.
Pour the mixture into 8-4 ounce canning jars and seal the lids "finger tight."
Place in the water bath (carefully) and cook for 1 ½ hours.
Remove and let them cool in the counter for 15-20 minutes.
Chill for at least 3 hours and serve straight from the jars.
Notes
Don't whisk too vigorously or you will get too many bubbles in your custard. You want it totally smooth. Pop any large bubbles on the surface.
You can also strain the custard mixture before cooking to ensure an extra smooth texture and eliminate any bubbles.
Mix in any additional flavors you want before pouring the custard in the jars.
Tighten the jars "finger tight." This means you tighten the lids until you barely feel it grab the jar. It should be easy to twist the lid back off with your fingertips.