Pit the cherries and place them in a glass container large enough to hold them, the vodka, and the sugar. Add the vodka and sugar to the jar. Shake to dissolve the sugar. Steep in a cool, dark place for 8 weeks.
Strain out the cherries and bottle the liqueur.
Notes
This will keep almost indefinitely, but I try to use it up within a year. Store the cherries in the freezer and spoon them over ice cream or add to cocktails.