Put the cherries, sugar and lemon zest and juice in a large skillet and stir to combine. Cover and cook over medium heat until the sugar dissolves, about 4 minutes. Uncover and cook until the cherries get juicy, about 5 minutes more.
Mix together the rum and kirschwasser in a measuring cup, then add to the cherries. Ignite the alcohol with a long match and swirl the pan slightly until the flames subside, about 30 seconds. Serve the warm cherries and their juices over ice cream.
Use extreme caution when igniting alcohol. Remove the pan from the heat source before adding the alcohol. Pour the alcohol into the pan and carefully ignite with a match or click lighter. Return the pan to the heat and gently swirl to reduce the flames.