You may be familiar with mason jars for their common use in canning. John Landis Mason designed this specific style of jar, which bears his name, in 1858. He designed it as a way to preserve foods without allowing bacteria to destroy the contents. This is still a common use of mason jars, but you can use them in other creative ways as well. You can, for example, bake bread or small cakes in mason jars. You can then consume them immediately or seal the jars and save the baked goods for later.
Preheat your oven to 325 degrees (unless your recipe dictates another temperature).
Place the jars and their corresponding lids and rings into a large pot. Fill the pot with water to cover the jars, then bring to a boil. Boil the jars, lids and rings for at least 10 minutes. This step is only necessary if you intend to seal the jars and save the baked products for later use; if you will consume them immediately, simply wash the jars, lids and rings with soap and hot water.
Grease the entire inside of each mason jar with butter or oil, then sprinkle flour inside to form a thin coating over the inside of the jar. Gently shake out any excess flour. This will help the finished product slide out of the jar more easily.
Pour the batter into the mason jars, filling each jar approximately ½ to 2/3 full.
Place the jars on a cookie sheet and put them into your preheated oven. Bake until they are done, probably 35 to 45 minutes. You can test for doneness by inserting a toothpick into the center of the baked batter then pulling it out. If it comes out clean, the bread or cake is done. If not, return it to the oven and check every five minutes until it is done.
Remove the jars from the oven. Place the lid on each jar, then screw it on with the ring. Allow the jars to cool. This should create an airtight seal, which you can test by pushing on the top of each lid. If the top is already inverted and does not give under pressure, the jar is sealed. If the top is raised slightly and gives under pressure, the jar is not properly sealed. Consume the contents of any improperly sealed jars immediately, as they will not keep. Skip this step if you are not canning the jars for long-term storage.