Blanch, peel and deseed the plums. Combine the plums, jam sugar and cinnamon sticks in a saucepan and boil for 3-4 minutes, stirring constantly.
Remove the cinnamon sticks and skim off the foam carefully. Stir the marmalade quickly. Leave a few small pieces of plum.
Add the rum to taste and boil for another 2 minutes.
Pour into warm, thoroughly cleaned jars. Seal. Store in a cool place.
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