Boil the water, add the long grain rice, stir and make 10 min. Add the milk and make another 20 min. Stir from time to time. Add the sugar, the vanilla sugar and the cornstarch mixed with a little water. Make it light for about 10 to 15 more minutes. Remove from heat and stir in the beaten egg yolk.
Put on heat again for 2 min and stir continuously. Pour into small bowls (portions). Serve cold, sprinkle with cinnamon if desired.