Chop the plums into quarters, spoon into ramequin dishes or a ceramic tart mold. Sprinkle with the cinnamon and vanilla sugar. Blend the almond flakes. Mix the almond powder, flour, butter and brown sugar into crumble. Heap the crumble topping on the prepared plums. Preheat the oven to 180ºC. Bake the crumble until cooked through and golden brown on top (for about 15-20 min).