Drain the liquid from the contents of the jar of cherries by suspending a strainer over a container or bowl.
Dis-card the liquid (or save it to use in another drink) and return the cherries to the jar.
Add the cognac, amaretto and maraschino liqueur.
Reseal the jar and shake gently to combine the ingredients.
Add a label with the date and store the jar in the fridge for at least one month before using.