Use only wide-mouth jars. Filling the jars can be tricky because you want the cakes to bake to within one-quarter to one-half inch of the rim. Make one test cake by filling one jar halfway to ensure you have the right time and temperature. Do this at higher altitudes, too.

For half-pint jars, use one-half cup batter and bake at 325 degrees F for about 30 minutes. For pint jars, use 1 cup batter and bake at 325 degrees F for 55 to 60 minutes. For 1 1/2-pint jars, try 1 3/4 cups batter and bake an hour or longer at 300 degrees F. A long cake tester is useful to verify doneness.

Adapt your favorite baking recipes to jars. Pound cakes or nut/fruit breads work best. Reduce the temperature 25 degrees because glass bakes hotter than metal.

Make sure there are no nicks or cracks on the lips of the canning jars. Wash jars, lids and rings in hot soapy water, then sterilize by boiling them for 15 minutes. The lids and rings are kept in hot water until you're ready to use them, but the jars are moved from the water and placed on a towel to air dry while you mix the batter.

The jars must be well greased with shortening or oil so the cake will slide out. After the cakes are done, you take them out of the oven, one by one, and put the lids and rings on them. Screw the lid tightly. As they cool on a bath towel on your counter, you should hear a "plink" sound indicating that they have sealed. If you don't hear it, check cooled jars by pressing down on the lid. It shouldn't move at all.

Refrigerate unsealed cakes or freeze them. Sealed cakes will keep in a cool, dry place for about six months. You can send one with a candle as a birthday cake.