Sterilize jars with hot water and allow to dry.
Place the cherries in a large saucepan. Trim both ends of lemongrass and peel tough outer layer. Flatten with a knife. Add to the cherries along with the jam sugar. Bring to a boil and cook until bubbly, while stirring continuously, about 4 minutes. Stir in the liqueur. Remove the lemongrass. Fill the jars with the cherry jam and tighten lids. Turn upside down for 10 minutes. Turn back and allow to cool completely. Store in a dark place. To preserve the jam for longer, you will need to process jars according to manufacturer's instructions, or visit http://nchfp.uga.edu/.