Heat the oven to 450 degrees or heat a medium skillet over high heat.
Place the cinnamon sticks on a small baking sheet and bake (or toss in the skillet) until they start to blacken in spots, about 5 minutes.
Remove the cinnamon sticks from the oven or skillet and transfer to a storage container.
Pour in the high-proof spirit and let soak for 24 hours.
Pour the mixture through a fine mesh strainer into a bottle and discard the cinnamon sticks.
Store the bitters indefinitely.