You can also add a whole cinnamon stick or two, depending on the size of your brew, during the last 10 minutes of the boil. Less surface area in the whole stick, leads to a subtler flavor addition than when adding the ground spice, and easier to gauge strength of flavor. You can leave the stick(s) in during ferment/secondary and remove when you have the cinnamon essence you desire. Less is usually more with cinnamon!