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Before you make your oil, sterilize the jars so that you don’t get any unwanted bacteria in your oil. Do this by using warm water and dish soap, followed by a bath in boiling water.  Start by removing the lids from your jars and washing the inside and outside of each jar and its lid in warm water. Use dish soap and rinse thoroughly. Once the jars and lids have been rinsed in warm water, transfer immediately to a boiling pot of water. Keep the lids off the jars. Make sure there is enough water to entirely submerge the open jars. Remove the jars and put them face-up on a clean baking sheet. Dip the tips of metal tongs into the boiling water for two to three minutes, then use the sterilized tongs to remove the jars. Allow the jars to cool before handling. If you are using cinnamon sticks, fit them vertically into the jar. Pack as many in as possible. For a quart-sized jar, you may want upward of a dozen cinnamon sticks.  If a stick is too long to fit in the jar, use a kitchen knife to gently saw the stick in half and pack both halves into the jar.  You may want to use new rubber or nitrile gloves while packing the jar in order to avoid transferring over any bacteria from your hands. Pour your carrier oil into the jar until all of the cinnamon sticks are completely immersed. If the jar allows, try to have at least half an inch of oil above the tops of the cinnamon sticks. Use a clean butter knife or chopstick to maneuver the cinnamon sticks if the oil is not flowing down to the bottom of the jar. If you are using ground cinnamon, you will cook it into the oil before placing it in the jar. Use about a quarter of a cup of ground cinnamon for every cup of your carrier oil.  Mix the two together in a sauce pan over a low-to-medium heat. Stir the oil and cinnamon until combined, then let simmer for three to five minutes before removing. Let cool for up to 10 minutes. Once the oil is cooked and cooled, place in sterilized glass jar and allow to steep. Tightly seal up the jars and place them in a warm, dry area such as on a windowsill. Leave the jars in place for up to three weeks. This allows the cinnamon to release its flavors and certain nutrients into the oil.  The longer you leave the jars, the stronger the oil will taste. Taste test the oil once every week or so, and allow to steep until it reaches the strength you want. Oil made with ground cinnamon can be used immediately, or may be left to steep for a stronger flavor. Try tasting the oil after a week, as ground cinnamon tends to need less time to steep. Shake the jar daily. This will help infuse the base oil with the cinnamon, and discourage any molding along the surface of the oil. Use a piece of cheesecloth to strain the cinnamon oil into another sterilized glass jar after it finishes steeping. Place the cheesecloth over the mouth of the new jar and secure it with your hand or a rubber band as you pour the oil in.  To get extra oil out, allow the cinnamon to fall into the cheesecloth. Then, twist the cloth tightly around the cinnamon to force out more oil. This may get messy, so it is best done over a large bowl or in the sink.
Sterilize the jars. Pack in the cinnamon sticks. Add in the oil. Prepare the ground cinnamon. Steep the oil. Strain the oil.