Comments: I have gathered this information from several different sources on the internet. I hope you find it helpful.

When making the "mix" recipes, keep this in mind: The first recipe is the one you make and put into the jar. The second recipe should be printed out in a nice font, maybe with a nice border around it, and attached to the jar.

A simple circle of cloth placed between the seal and the ring (of a two-part canning lid) makes a pretty effect and you could also add a ribbon around the ring. (Use scissors to cut a 9 inch-diameter circle from cloth of your choice. Place over lid and secure with rubber band. Tie on a raffia or ribbon bow to cover rubber band.) You can add a piece of cotton under the material to make it a little puffy. A hot glue gun is a very useful tool to have! You can glue on dried flowers, ribbons, dough-art... you name it, it can be glued onto the lid, ring and side of the jar.

Preparation of Jars for the "Baked in a Jar" Recipes.
Use Wide Mouth jars and ONLY use jars meant for canning, not old mayonnaise jars. They also make "plain" jars (no diamond pattern). Wash jars in hot soapy water, rinse in hot water. Put jars and new lids in kettle with hot water. Bring to a boil and boil at least 10 minutes to sterilize. Use only new lids.

To grease jars (or pans) for baking, use a mixture of equal parts Crisco, oil and flour; keep a small jar in the fridge and brush it onto baking surface with a pastry brush. Be sure not to get any grease on the rim of the jar. This would prevent the lid from making a perfect seal.

After taking the jars out of the oven and putting the lids and rings on them, place in a location away from drafts. Do not move until completely cool. This could disturb the sealing process.

There will be a little condensation on the lids and some in the jars so when you seal them it's trapped inside. Don't worry about getting the water off of the lids before placing them onto the jars, the added moisture doesn't hurt the cakes in the slightest.

A jar is sealed when it pops and the center is indented a little bit.

The jars do seal, just like any canned good. You don't have to refrigerate the jars, just keep them in a cool , dark, dry place. Check the jars occasionally by pushing down on the lid (in the middle) if you're storing them for your own use; if the lid moves up and down, that means the seal has broken. If you've checked the jars frequently, more than likely they're safe to eat; otherwise, toss the cake. If you give the jars away, be sure to tell the person to check the jar periodically (if they plan on storing it for any length of time).

Are the cakes easy to get out of the jar?
As the sides are straight up and down, the cakes slide right out. If the place where you've stored the cake is really cool, you may need to warm the jar up a bit--either hold it in hot water, or pop it (minus the lid) into the microwave for 1-2 seconds and slide it out. Store any leftovers in the jar with the lid on, and pop it in the fridge. Once opened, they need to be eaten within a day or two or refrigerated. As the sides are straight up and down, the cakes slide right out. If the place where you've stored the cake is really cool, you may need to warm the jar up a bit--either hold it in hot water, or pop it (minus the lid) into the microwave for 1-2 seconds and slide it out. Store any leftovers in the jar with the lid on, and pop it in the fridge. Once opened, they need to be eaten within a day or two or refrigerated.

What else can be baked in canning jars?
You can bake any quick bread type cake in canning jars. (Regular cakes don't work; they tend to fall when the jars seal.) The only thing you have to figure out is how much batter to put into each jar. Most recipes work by filling them 1/2 full. Some batters will rise higher than others. I'd suggest filling one jar 1/2 full and baking it. If it rises to within 1/4 to 1/2 an inch from the top of the jar, it'll work fine. If not, adjust accordingly. Experiment with your favorite quick-bread recipe, and once you figure out how much batter to put into the jars, write it on the recipe so you won't forget.

The baking times will vary--the moistness of each cake recipe will determine the time. Most of the recipes bake in 35-40 minutes. Start checking the cakes at 25 - 30 minutes and go from there. Don’t bake these jar cakes over 325 degrees F.