Drain the plums and collect the juice. Boil up the juice and sugar. Stir starch with a little water until smooth and bind the juice with it. Fold in the plums and let them cool down. Place the brioche slices on a baking tray and lightly toast in a preheated oven (electric range: 225 °C/ convection oven: 200 °C/ gas: level 4).
Beat the eggs, 200 ml milk, salt and vanillin sugar. Turn the brioche slices briefly in the egg milk. Layer with the plums in a greased casserole dish. Pour the rest of the egg milk over it. Sprinkle with almonds.
Bake in the oven at the same temperature for 20-25 minutes. Put cream, 125 ml milk and sauce powder in a bowl and whip for about 3 minutes. Sprinkle brioche casserole with cinnamon and sugar. Add vanilla sauce.