I bake fruit and vegetable breads in canning jars. Examples are zucchini bread, banana bread, and our fall favorite chocolate chip pumpkin bread. I told this to a friend and she tried it. She wasn't successful. When I saw what she did I just laughed. Rule #1 when canning breads, use a wide mouth straight sided canning jar. If you use a jar that has a taper up at the top your bread will not come out in one piece. It will make good bread pudding though!
Put a light coat of grease (I use Crisco) in the jar to cover the bottom and sides. Do not bring the grease too close to the rim or get any grease on the rim of the jar. Make your recipe as normal and pour your batter into the jar rather than baking it in a loaf pan. You will need to experiment to know how much to pour in. You want the top of the loaf to come just below where the lid would be if the lid were on. Do not bake with the lid on!
As soon as it is done baking take it out of the oven, wipe off the rim, then put on your canning lid (that you have prepared in hot water) and loosely tighten the ring. If you put in too much and the loaf bakes up higher than the top of the jar that's ok. Just cut off the top of the bread so it's below the rim. Let the jars sit on the counter to cool just as you would when canning fruits and vegetables. It's really that simple.
When it's holiday time I give these jarred breads as gifts. I usually put a puffy decoration on the lid, which was really popular during the 1980s. It's a well liked gift but often during the holidays people have so much to eat that they throw away a lot of food that sits around and gets stale. If the person isn't going to eat it right away it will be preserved and they can enjoy it at a later time.