Cut the bread roll and peeled rhubarb into slices. Pour hot cream over the rolls to soften them and stir with a spoon. Mix sugar, egg yolk, vanilla sugar and cinnamon until foamy, stir well with rhubarb slices and softened rolls. Finally, carefully fold in the stiffly beaten egg white. Butter a baking pan well, pour in the mixture and cover with flakes of butter. Bake in a preheated oven at 160 ° - 200 ° for about 45 minutes. Cream or vanilla sauce whipped with powdered sugar also tastes good.