Portion 1/2 cup of ice cream into 4 serving bowls, and freeze until ready to serve.
If using fresh cherries, wash and pit the cherries.
Wash the outside of the lemon with water. Finely zest the lemon with a zester or on the smallest holes of a grater.
Combine cherries, sugar, lemon zest, and the juice from half a lemon in a small frying pan, and heat on the stove, over medium heat, until sugar dissolves and the cherries start to soften and release their juices (about 5-7 minutes for fresh cherries, and about 8-10 minutes for frozen cherries).
Remove the pan from the heat and add the rum. Ignite the rum with a long lighter or a match held with tongs. Gently swirl the pan until the flames subside (about 30 seconds).
Serve the cherries and their juices over the prepared ice cream, and enjoy!