Wash the mountain ash berries and drain well. Strip them from the panicles. In a bowl, lightly mash the berries with the crushed brown rock candy. Cover and let stand overnight.
The next day, crush the cloves and cinnamon stick in a mortar. Transfer the berry mixture and all its juice to a large glass bottle. Add the crushed cloves and cinnamon. Pour the schnapps (grain or brandy) into the bottle. Seal the bottle tightly and place in a bright location away from direct sunlight. Let stand for 3 months, shaking every few days.
Strain the mixture. Transfer the liqueur to clean bottles and store in a cool, dim location for 8 months before serving.