Wash the mirabelle plums and pit them with a plum stone. Put the cinnamon and preserving sugar in a saucepan and stir well until the sugar slowly dissolves. Then add the Schwips (gin or mirabelle liqueur) and bring to the boil for about 4 minutes.
Chop up a little with a hand blender, bring to the boil again and pour hot into prepared twist-off glasses up to 1 cm below the rim. Screw the jars on tightly and let them stand upside down on the lid for 5 minutes.