Known in Italy as "Marasche al frutto" (literally 'cherries to the fruit'), these are the Marasca cherries used by Luxardo for distilling its renowned...
Not quite the same, but I enjoyed making my own from unsweetened morello cherries, marinated with 50% 2:1 sugar syrup and 25% each Armagnac and Luxardo liqueur, from memory. Not quite the intensity of flavour of the commercial ones, but I thought successful and a suitably aromatic and tasty garnish.