Drain the plums in a sieve, collecting the juice. Coarsely chop the walnuts. Stir pudding powder, 50 g sugar, cinnamon and 100 ml plum juice until smooth. Bring the rest of the prune juice to the boil, stir in the pudding powder, bring to the boil while stirring and simmer for about 1 minute. Stir in plums. Pour into an ovenproof casserole dish.
For the crumbles, put flour, 100 g sugar, vanillin sugar, salt, egg yolk and butter in flakes in a bowl. Mix with the dough hooks of the hand mixer, then work into crumbles with your hands. Spread the crumbles on the plums. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 25-30 minutes. Remove from the oven and dust with icing sugar. Serve with vanilla ice cream
With 8 people: