Make a shortcrust pastry from the flour, margarine, sugar, salt, egg and milk and place it in a greased springform pan. Pull up one edge.
Bring the plums and cinnamon to the boil and whisk with the hand blender.
Mix the vanilla pudding with 2 tablespoons of sugar and the water. Stir the pudding into the plum sauce and bring to the boil. Once cooled, spread the pudding onto the shortcrust pastry.
Make the crumble from flour, margarine, sugar and nuts and sprinkle on the cake.