Knead a shortcrust pastry from 200 g flour, the egg, 75 g margarine and 75 g sugar and line a springform pan with it, forming a high rim. Prick the dough several times with a fork.
Hang a sieve over a measuring beaker and let the cherries drain off. Make up to 500 ml of the juice with water. Remove some juice and mix with the pudding powder until smooth, heat the remaining juice and pour in the mixed pudding powder while stirring. Bring the pudding to the boil briefly and then let it cool for about 5 minutes. Spread the cherries on the shortcrust pastry and pour the pudding over it.
Mix 100 g margarine, 100 g sugar with the cinnamon, hazelnuts and 100 g flour with the dough hook of the food processor. Sprinkle these on the cherry pudding.
Bake in the oven at 175 degrees for about 60 minutes. Let the cake cool in the mold and then put it on a cake plate in the refrigerator for about 3 hours. Whip the cream until stiff and, if necessary, spread 1 packet of vanilla sugar on the cake. Sift cocoa over the top before serving.