Like ceramic ramekins, glass jars can withstand the low oven heat needed to cook custards and brown the crust on a pot pie. We recommend placing the jars in a hot water bath to regulate the temperature - just set the jars inside a casserole dish or roasting pan and fill the pan half way up the sides of the jars with warm water.
Wide-mouth half-pint canning jars would probably work best for these purposes. They're easy to fill and make just the right serving size for one person. Plus, storing leftovers is a simple matter of screwing the lid back onto the jar!
Give it a try!