Core the plums and cut into small pieces. Bring to the boil with the sugar, cinnamon and water (up to 6 tablespoons) and simmer until the plums are soft. Puree the plums. In the meantime, mix the pudding powder with the 6 tablespoons of water and mix with the plums. Bring to the boil again while stirring and pour into clean twist-off glasses, screw on the lid immediately.
The pudding can be kept for about 3 months.
Of course, the pudding can also be eaten straight away, but I like it as a reserve for a quick dessert.